I have owned both, and unless you want to do extensive modification to the DQ10's, the DQ20 is much better at everything. The DQ20i (which is biamp-able) is even better than the DQ20 - until recently I had a pair of each. The difference is subtle, but I find the DQ20i mids to have a bit more detail and slightly better imaging. Though imaging with either model is spectacular if you're in the somewhat small sweet spot.
Both are great speakers which don't give up much, except in bass slam, to much more expensive "modern" speakers. I've a/b tested the 20i's against the Alon V's and much preferrred the 20i's. There are speakers with flatter measured frequency response, but I haven't heard ANY, including some very expensive ones, that reproduce the timbre of individual instruments and voices as accurately.
Also note that if the woofer surrounds are original, they will likely need replacement in the near future. No big deal (you can do it yourself in about 4 hours if you are reasonably skillful) but be aware of that.
