Sounds like you're building into a nice setup. But several concerns come to mind. Most speakers that would be practical in rooms like you're talking about will put out a sound level in the 80-90db range, measured with a mike one meter from the front of the speaker, with an input of one watt. (Yes, one watt.) How that translates into the level in a normal size room depends a lot on how much sound is absorbed by the furniture, wall and floor surfaces, etc. With concrete walls you're going to have very little absorption and a lot of reverberation. In fact that will turn out to be a problem if you care at all about quality. So at least in your HT space I think you will NEED some sound-absorbent surface treatment, especially in the corners. As for the difference between 75 and 125 watts per channel: assuming one speaker with a sensitivity of 85db, a 75-watt signal (a brief peak, I hope) will give you about 104db and a 125-watt signal will give you 106db. Some difference, huh? And, at ordinary listening levels where our hearing is most sensitive - say, in the 70-db area - we have to strain a bit to even notice a 2-db difference in sound level.
My point is that there may be valid reasons for preferring one amplifier to another, but a power output difference of 2 db is not one of them. Put your money into room treatment.