Whoa there. Far be it from me to tell you how to spend your money, but if it was me, then I'd want to know why the 7011 and Tannoy combo isn't working before doing a scatter gun approach of throwing around chunks of cash at randomly suggested solutions.
I've had pretty decent stereo performance out of some relatively modest midrange AV receivers paired with speakers that are quite revealing. By that I mean being able to tell the difference in sound between cheap analogue stereo leads and something better, and those versus digital coax, and running the source in pure 2 channel mode, and the receiver being switched between standard and pure stereo mode too. Some of these are nothings you might expect a £700-£800 AV receiver to resolve.
As a general rule of thumb with AV receivers, the internal DAC stays in circuit unless the receiver has a pure stereo mode for analogue. My TAG McLaren AV pre-amp had that. In bypass mode it was simply an active analogue pre-amp.
Coming back to your Marantz/Tannoy/Chromecast combo, there are so many places where the performance can be borked that anyone offering fixes without first going through your existing setup is really just working in the dark.
Some initial questions:
- Have you had good stereo performance from the Tannoys where they currently sit but using a different amp and source?
- Have you had a listen to your system with a decent CD player as a source?
- What difference do you hear in sound between running the 7011 in pure mode versus running it with room correction engaged?
This is not an exhaustive list, but it goes to the heart of speaker/room set up, and source quality, and whether there are other factors getting in the way of your system performing as it stands that would then mean spending any further lumps of cash would be a futile path.
Something as simple as running the speakers from a receiver in bi-amp mode can quite easily mess up the sound. Not to mention of course that a Chromecast at £30-ish as your main audio source could well be the bottleneck strangling the whole system.
