After about a month of research, calls to Polk, emails and calls to tech reps and some interesting discussion on the Forum, I ordered Sonicaps for my SDA-2 crossover upgrade. I purchased 0.1 uF (Gen II), 0.47 uF (Gen II), 12 uF and 27 uF (Gen I) capacitors, 2.7 and 3.5 ohm 5 watt Mills resistors. I decided to go with the Sonicaps after discussion on the Forum and several articles on Sonicaps and two long conversations with Jeff Glowacki at SonciCraft. A great guy that will spend time talking with novices like me about this subject. He was very good about explaining the function of capacitors, how they were built, what differences that I would hear with various capacitors. Stand up guy! I can't say enough good things about him. Based on Jeff's advice, I decided not to use a 750 pF by-pass capacitor around the 0.47 uF. I was going to buy 4 750 pF Relcaps and use alligator clips to perform a sound test with and without, but Jeff talked me out of it. For one thing it would take several hundred hours to break in the caps and Jeff was adamant that I just wouldn't hear it. Especially at my age (52), I just wouldn't notice any subtle changes in the very high frequencies. Not only that , I've probably fried my ears with loud music ever since I was about 12 years old listening to the Stones.
The big step here is to use a 0.1 uF bypass on the 12 uF . The 0.1 uF is more than 100 times (if I did the math right ) the 750 pF. I know Jesse has ordered one to try it out. I'll be very interested in his findings. Jeff felt strongly that 1) definitely need a by-pass for the 12 uF 2) 0.1 uF was a good value to use.
Don't expect a report on this upgrade any time soon as I want to utilize my brother's soldering skills over mine. This is his busy season so I don't expect to capture him for several weeks. I know several Forum members are very interested in this topic since most of the crossover upgrades have been done with Solen caps and the Sonicaps cost significantly more.
The total cost for the caps and resistors was $260. Binding posts and solder another $40. Total cost of upgrade $300 plus dinner for my brother and he's a big eater.
I will report on this project after I complete it and spend some time doing some critical listening. If your interested in an article about Sonicaps, check out this link: http://www.10audio.com/sonicraft_vh-oimp.htm The article evaluates the performance of a 12 Uf Sonicap. I have two of these in my crossover. Sone other SDAs probably have them as well.