I have about 1 minute of time, and most likely cannot respond for the rest of today. Good luck during my absence.
I first started learning about cabinet resonance with WmAx's postings. Yes, I think floorstanders (and subs) present much greater issue. But, it's still an issue with bookshelves, if much more curtailed.
10 years is a long time. You have got to find a way to bring in some contenders to your place. Try Salk, Ascend, others. Ask your dealer if you can borrow a pair to compare. If he says no, then forget him, and ask someone else!
You can try asking WmAx for the 10 step instructions for cabinet mods to the Ascend 170SE. $260 as b stock is a really great deal on these. However, 170SE will have limitations with both power handling and extension. Higher sensitivity than the Sierra1s, IIRC.
With 2k (is that right) for the budget, you can buy a pair of those, a pair of Ascend Sierra1s, as well as some Salk bookshelves all at the same time. (well, I'm pretty sure you can, Salk page is not loading for me). Send back the losers.
Sorry I can't be more helpful, atm, I really have to run. Cheers man.