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
but it would more than ok in your basement (at least until the upgraditis bug strikes