It depends on how big your room is and how far are you sitting from the speakers.
7 responses Add your response
I'd get some with a highish sensitivity of 90db or so and of good quality. You lose 3db every 3' you sit back from the first meter on a point source. Also the room acoustics play a significant role. If you have alot of overstuff furniture and carpeting it will probably have better acoustics but not quite as loud than hardwood floors etc. It can be done easily though if the speakers are upto it. Having a sub will help alot.
To Warnerwh: My understanding is that SPL falls off by 6 dB with every doubling of distance from a point source (assuming anechoic conditions). In a reverberant environment like a living room this holds true over fairly close distances, but then as the distance increases the reverberant sound will bring up the SPL by a few dB over the predicted anechoic level.
Sound pressure level falls off by 3 dB for each doubling of distance from a line source under anechoic conditions, and once again in a reverberant room the fall-off is a bit less than the anechoic prediction.
Measurements I've taken support these figures.
It sounds to me like your amp is running out of gas. If your average is 90dB, your amp is probably clipping on peaks, assuming your speakers are roughly 87dB sensitivity. 100W would give you a peak loudness of 107dB, i.e. 17dB of headroom, which could clip on peaks. This is not bad performance, you're just pushing the limits of what your gear can do.