Sound quality wise is there much difference between the two? Any opinions from people that have heard both would be appreciated.

I don't think the MC-8 offers LPCM over HDMI so that alone would be the deal breaker, unless lexicon came out with another firmware update.

I began with an MC-8Bv2, then recently replaced it with an MC-12Bv5 (not the HD version).

In my opinion, the EQ does make a difference (though in my instance my room acoustics are good and the difference is very slight), the ability to have two subs was a positive, and the higher grade DACs bring a slightly better sound quality to 2ch and other.

That said, the MC-8 is very high quality and if your room acoustics are good it will perform admirably.

Sound quality wise is there much difference between the two?The MC-12 has dual-differential DACs for each channel, giving it a slightly cleaner output (S/N ratio and THD+noise) than the MC-8. However, the biggest difference in sound quality is due to the MC-12's features. Room correction helps tame frequencies with long decay times, which improves clarity since quiet details are no longer masked by lingering sounds. Multi-sub support gives you the flexibility to use up to 3 subs in order to get more consistent bass across multiple seats or maximize low frequency envelopment (stereo bass), as well as use different subs for derived bass (filtered from other channels) and discrete bass (from the .1/LFE channel on the recording). The MC-8 doesn't have either of these capabilities.

Sanjay