Eleonida: Good questions, but no hard fast answers. I have tried out some speaker/amp combos that looked good on paper as far as the manufacturers specs for the equipment went, but that were a total bust. I am running 90db, 4ohm speakers with a 7watt per channel tube amp and the low ohmage does not seem to add the dreaded flab to the bass response, it sound great. I tried running a pair of Linn Tukans with a 50 watt/channel (70+ in reality and 140+ into 4 ohms per the review specs) SS amp and it would not control the low end of the 4 ohm Tukan's. The same amp ran a pair of Reynaud Twins (also 4 ohms) fine. Either the specs are wrong or there is more to it than the numbers. If you can, go for 90db (which is fine) or more (it's a nice range for many amps and rooms), but try to home demo the speakers before you purchase them. If this is not possible then hookup with fellow listeners that have your amp and see what has worked for them. Perhaps list your complete system (with the room size and your current speakers) in this or a new thread and list what you would like to improve. I can't imagine that mismatches like this are commom place, but they do happen and I would hate to see you stuck with one, especially with your wife watching/hearing. I purchased my amp (not my speakers) without an audition, but did so after checking it out with other owner's that I located on the web and everyone else that ever wrote a review or commented on auditioning it.
Sensitivity Issues
I'm on the hunt for a speaker upgrade. My current amp is, well, modest (30 wpc Pass Labs). I've been advised to confine myself to sensitive speakers (more sensitivity in the house has cheered my wife). What range am I looking for, and how big a difference is there in a couple of db's, say 89 and 91? Also, if I drop down in resistance (8 to 6, or even 4 ohms), does this compensate, or do sensitivity figures already take resistance into account?