I completed the crossover upgrade on my SDA 2B's last night. I used Sonicaps for the high pass filter (12 uF GenI) and associated bypass (0.1 uF GenII), Solens for the shunts in the low pass filters (20 uF and 39 uF), and Mills MRA-5 2.7 ohm resistors. Thanks to DarqueKnight for the schematics and to BlueMDPicker for the excellent step-by-step instructions in the thread "SDA 2B Studio Crossover Upgrade" (http://www.polkaudio.com/forums/show...sover+upgrade).
I immediately noticed a subtle but definite improvement. They sound smoother and cleaner from top to bottom, more open and detailed mids and highs, more realistic vocals, more precise imaging, and larger soundstage. These changes are not dramatic individually but the combination makes a difference. The biggest difference I noticed is that there is no longer any listener fatigue associated with the highs even though there is more detail. It's hard to completely describe the overall difference but it's a little easier to forget you're listening to speakers and they're simply more enjoyable to listen to.
There has been some discussion about using all Solens or all Sonicaps versus Sonicaps for the high pass and associated bypass and Solens for the low pass filters. I can't say how much if any difference there would be using all Sonicaps but I definitely don't hear any negative results from the combination.
On a side note, there are three different schematics for the 2B crossovers (1987-bb, 1987-pb, and 1989). Mine have the 1987-pb (pin-blade) crossover. The only difference between 1987-pb and 1989 is the polyswitch. 1987-pb uses RDE050A and 1989 uses RDE090A. I've never had any problems with them but am curious if anyone knows the difference between these two and why Polk changed them.