Thanks for your comments TLi. I think the new Vitus SIA-030 has enough power (conservatively 400 watts true RMS @4 ohms) and total capacitance (616,000uF) to control the M6's.
Re: room size, when you calculate 1000 sq ft, are you calculating by L x W x H? As i've always gone by small Room <1,500 ft3. Therefore <1,500 ft3 I'd recommend the M2 or S3 Mk2, Medium Room 1,500 ft3 - 3,000 ft3 I'd recommend the M3 or S5Mk2, large Room 3,000 ft3 - 5,000 ft3 I'd go with either the M6 or S7. Correct me if i've got my figures wrong.