There will be some similarities since Melody has a certain design philosophy and only deviates so much in their different models, but these are definitely different. You heard the
AN300B at Richidoo's, which was 22w class A push-pull via four 300B's. There is no mono version of that amp.
The M845's are 21w class A single ended via a single 845 per side. They will be a touch smoother at the top end and have a slightly sweeter, more liquid sound. That comes at the expense of a little bottom end control, although it's still pretty good for a relatively high power SET amp. Of course there is also the benefit to having monoblocks with separate power supplies and completely separated signal paths. The photo above from CAS in July shows the two M845's and the Pure Black 101 preamp.
They are priced similarly, with the AN300B at $5679, and the M845's at $5899, although buying monos necessitates a separate preamp. During the show of course both would be 20% off at $4544 and $4720 respectively.