I ran my D5's without any problems with my Denon 2307. I like my music loud and they sounded good. Any decent mid-level receiver should be fine, say an Onkyo 805, etc. If your wife is a rocker, she might appreciate the D5 over the D4, although it's a bit more money. It's a little fuller sounding with a stronger bottom end, easy to integrate with a sub. I've said it before, I pound the living crap out of these speakers with everything from Metallica to Rage Against The Machine, Black Label Society, Rush, Black Sabbath, etc. and they take whatever I throw at them and keep sounding great the whole time.
I did have the chance to borrow a good external amp to test it out and did see some improvement at really high volume, but you don't need it especially if you're going to use a sub. Down the road, if you wanted to add an external amp, you can be confident that they will take the power you want to throw at them with no trouble.