Too add an amp later on, the AVR must have pre-outs and unfortunately most budget AVR lack this feature. Watt are not linear to power - To double the volume (+9db) you'd need to 10 times the power.
As long as speakers present easy load, with 75 (Denon) Watts - you should't worry about power.
Now, you're not going to able to use this amp to play for large crowds in large venue
![Smile :) :)](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)
but it would more than ok in your basement (at least until the upgraditis bug strikes