SONY Power Amp question:

I guess that depends how loud you want to listen. They are 88dB @ 1watt, so that's 108dB at 100 watts. Since the Sony you say is 120 watts, I'm assuming that is into 8 ohms and the M5's are 6 ohms, for me, I would get more power. I think the biggest improvement would be to separate your 2 channel system from the surround system.

Yes it will run your loudspeakers but the SQ may be less than ideal (consumer grade HT receivers are not known for great SQ). 

thank you for your response .

As an S-master Pro design it will sound a bit better than ordinary digital HT receivers but consider that this was an entry model of the series. Going up to DA5000es, DA7100es and DA9000es there is more juice in terms of sound and power in 2ch.
But it will drive your speakers at satisfactory levels.

Well sound will come out. At low volume might be OK.