I don't mind the sound of the MCA, but if I could get a more sweeter sound from upgrading to a better class of amp then I would consider it.
Having done an instantaneous A/B test of a few amps and receivers in my past, including Parasound Halo, Onkyo AVR, a Robertson tube and a Coda (about $4k retail new), this concept of massive sound differences let alone 'improvement' between amps is seriously overstated. If you ever have the chance to do such a matched, blind comparison, it is unlikely you would ever hear a sound difference between two quality amps with all other variables the same (e.g. SPL matching as amp output to signal ratio may vary).
If you like to turn up the sound more than what the MCA can offer, then a beefier amp may be necessary, certainly. In the $3k range you will find TONS of possibilities and no, mono amps are not required unless you are going for a feng shui look in the room and want to balance left and right visually without placing a single unit/amp in the centre.
Anthem also sells their Statement line which are far more beefy than the MCA series.
http://www.anthemav.com/products-current/collection=statement/model=p2/page=specs
