I want 2.1 or 3.1 max at this moment in time. If my circumstance change I'll have the spares.
The limiting factor with either solution is going to be the speakers. If it's the Mission M3 kit you've got, then they're designed as AV speakers rather than miniaturised Hi-Fi speakers + sub, so I wouldn't spend too much time worrying AV amp versus stereo amp, particularly as it's mostly for TV use and a "4K player" which I'm guessing could either be a streamer or a disc spinner.
For the sake of clarity (no pun intended), a stereo amp will have the edge sonically of course. But whether you really hear much of a difference once everything else is taken in to account is very much a different question. What's perhaps more important is the sound from either should give the Beam a decent kicking.
What it comes down to then is the rest of the package. That means what it's like to live with day-to-day.
The Denon will get its signal from the TV via Optical, so there's no control signal via that. It has a remote control, but as a Hi-Fi amp it's very unlikely that the remotes from any of your other devices will speak "Denon PMA-600" IR code to operate the volume. You'll also need to remember to turn down TV volume all the way before using the amp. The TV won't do this for you automatically. Neither of these things might be that big a deal for you, but it's a PITA to find out these wrinkles after you've made a purchase.
An AV receiver, particularly one with HDMI ARC (as long as your TV is compatible) can be set to use HDMI control so that volume is unified, so is power on/off, and maybe input sensing too.
Setting up the AV receiver, you have the option to go 2.1 or 3.1. The receiver will adapt to the speaker configuration and deal with any rear channel info accordingly. This brings us back to speakers, and specifically speaker positions in your room.
The BMR drivers in a M3 kit are reputed to have a fairly wide dispersal compared to more conventional Hi-Fi speakers. That's really useful when you can dot the speakers in the locations where you want sound from, but the Achilles heel is their relative inability to create a convincing stereo image. That's quite important if you've got the speakers hooked up to a stereo amp and hoping that they image well enough that voices sound like they're coming from the TV rather than the speakers 3ft either side of the screen. This is where having the ability to run a centre channel speaker pays off.
Other AV advantages -
* the facility to tweak the centre channel volume relative to the L&R to give a bit more prominence to dialogue if required
* retaining DTS and HD audio if routed through the receiver first and so avoiding the downscaling bottleneck of the TV
* Night Mode
Now let's talk about power (Hornetstinger's 2nd favourite topic because he owns power amps)
No AV receiver will match the colossal power of big power amps. Neither will a £400 integrated amp, so let's forget these impossible comparisons. Both the AV receiver and the stereo amp will have plenty-enough power for what you need, and that's really all that matters.
The Denon sucks a maximum of 190 W from the wall socket. That's its consumption power rating. The speaker power output is given as 45 W in to 8 Ohm (20 Hz - 20 kHz, T.H.D. 0.07%). That's fairly conservative but realistic. The low THD tells us that the amp isn't working that hard, which explains the difference of 100W between the balls-to-the-wall maximum of 190 W compared to ticking along 90 W combined.
Now let's look at a £300-ish AV receiver. A Pioneer VSX933 was the first I found closest to that price point. Its max power consumption is 450W. It has 7 channels of amplification.
Pioneer rather optimistically rate the amp at 135 W/ch at 6 ohms, 1 kHz, 1 ch driven of 1% THD, but that's a bit of a work of fiction. 1kHz is a test tone, and who listens to test tones? 1% THD isn't a disaster, but the amp is working a bit harder than the Denon's 0.07% THD. 1 channel driven, another cheat: We can't expect the amp to sum up all its power from the transformer and capacitors and stuff it in to a single channel. It would blow the output transistor pair for that channel, but running one channel rather than two probably gives a 10-20% helping-hand to what the amp would deliver in stereo mode. The other cheat is measuring at 6 Ohms. The 8 Ohm measurement would be closer to 100W, all else being equal.
Working things back then, the Pioneer is probably pushing 30-35 W/ch in 7 channel mode measured in a like-for-like way with the Denon. That gives us a combined power output of 210-245 W. If we say that the amp is running in stereo though, and we take a 10% contribution from the remaining undriven 5 channels, then we can top-up our front channels to 45-52.5 W. What was the Denon again?
Before there's a huge outcry and wailing and gnashing of teeth, I'm going to throw a hand grenade in to my own argument and remind everyone that the PMA-600 will have a better quality transformer (both are ELs but still) and I dare say there's more microFarads of capacitance in the Denon, o it can probably deliver a bit more current swing. But.... the power disparity between a reasonable AV receiver and a stereo amp isn't the disaster some would like you to believe.
How much power do we actually need?
The Mission satellites are rated at 86dB/W/m. That means they're kicking out 86dB of sound when measured from 1 metre away and fed with just 1 Watt of power.
Reference level for cinema sound is 90dB. To hit that with a speaker rated at 86dB/W/m would require 2.5W. With either amp, we have a lot more power on tap than 2.5W. Okay, it's hand grenade time again. Sound dissipates over distance, so the amount of power required will increase. If you're sitting 3m away from the same speaker, then to hit reference level at that point requires 25 Watts for that channel. However, we're not finished.
Playing two speakers together means that the sound pressure level combines, so we need less power. We need about 12W per channel in stereo mode. We get another helping hand when we add the boundary effect from the back wall a couple of feet behind the speaker. Now we need about 6W/ch. Add a centre speaker and our power requirement drops to 4W/ch
It turns out then that we don't really need that much power to make a decent sound level. I'm going to throw in yet another grenade and remind you that speakers aren't a static load and having some extra power for headroom is never a bad thing yadda yadda yadda. However, all things considered, an AV amp would do okay for what you need.
