Many would also add a soundcard with the desired output format if the motherboard did not have it.
I take it your looking at an HTPC type specification? Music or Movie? Stereo or surround?
What video inputs has the projector got that you prefer to use?
Anything your recycling from the old PC? What sort of budget are you considering as cheap?
What CPU, memory, PSU etc do you already have?
Really hard to say what motherboard without seeing what you had, and how you configured and used it I guess.
AMD may be cheaper, as could shopping around. But to put it into context, years ago I only used PC's for music, but decided to build an HTPC gaming system, the best choice for gaming then was a dual core CPU and 4gb of ram.
That E8400 CPU with a passive Silverstone cooler, Asus Maximus Gene, 4gb Dominator GT, with a silent no fan HD-5750 GPU, 450w psu, BluRay drive, various HDD's sat in a Silverstone GD02 case for years and was my primary BluRay player, audio replay, and occasional gaming system, near silent but occasionally the case cooling let the system down, the Samsung BR drive would overheat, and it ended up requiring a few small fans for gaming.
Most of that old kit will still perform well enough to be used for BluRay and high res music.
Maybe your old system could simply be revamped? A sound card and video card, with an SSD or such, maybe new quieter case etc?
Gigabyte H81M-HD3 has an spdif out but requires an 1150 socket cpu, Pentium would be fine. Gigabyte H170N-WiFi is another option, but yor looking north of £100 in most cases with newer models.
My basket at Overclockers UK:
Total: £975.37
(includes shipping: £14.10)
I never realized so many features were being dropped in motherboards, even this old system below has HDMI and SPDIF output.
Asus P5QL-VM EPU motherboard
Intel E8400 CPU
Corsair XMS2-6400 2x4GB DDR2
Corsair VS350w PSU
Samsung DVD/RW optic drive
Fractal Core 1000 Micro ATX case