SONY Power Amp question:

Sony STR DA 3000es ....
Will this Receiver be powerful enough to run Mirage M5 IS Speakers in 2 Channel only ?
Sony is 120 RMS Per Channel.
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). 
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.
Do not feel the Sony will come close to seeing what these speakers are capable of. I paired these with a Rotel 990 series power amp. Match made in heaven with tremendous low end grunt. The 990 had a huge power supply with great power into low impedance loads.

It was always amazed how the 5si's, using two generic 6 1/2" drivers, could handle all that power and produce such palpable bass down to 30hz!