Noob to separates

Recently decided to jump into dedicated components rather than an all-in-one receiver solution. I've acquired some Wharfedale Opus 2-2's (plus the tri-center match) and from what I've read my Pioneer Elite simply won't do them justice even at 140 watts/channel. So. Now I'm looking at a five or seven channel amplifier in concert with my Pioneer VSX 74 as a pre-amp until I can pony up the cash for a bonifide pre-amp. After calling around and reading some threads it appears I'll need a good amplifier so that the Wharfedale's can sing since they are rated as 6 ohm speakers needing anywhere between 100 and 500 watts of clean power. Because I'm totally new to this, I need some advice as to what I can do.

How can I tell if I lack power? I ask because I'm not sure -- I read the manual, etc, but is there something I can do?

OK -- good advice. Is loudness a good indication of quality, or would one expect to hear attenuated subtleness not otherwise heard with clean power? I mean, would you hear all things that were meant to be heard with an A/V receiver, or would the dynamics change to incorporate a better range that might otherwise be lost if the speakers weren't driven with an amplifier? If not, and it's strictly a measure of loudness, then I'll just stick with the receiver after borrowing a dedicated amplifier and then wait to see if I notice a change.