Calling all passive bi-ampers

Not necessary. The amp responds to the load. The coupling cap is to block DC and may not be necessary at all, depending on the preamp. If you have an old Counterpoint, leave it.

That's exactly how the high-pass section of a Dahlquist DQ-LP1 Passive/Active x-over functions, though it may be necessary to add a resistor in parallel for proper alignment. Your amplifier is processing a full range signal otherwise, which is then blocked by the speaker system's crossover. If you can locate the DQ-LP1 users manual, it contains all the necessary info/formulas for proper 1st Order Butterworth Alignment(6db/oct roll-off) per what you are considering. This site has some good info on the DQ-LP1 starting on page 13. No formulas though. You may try contacting AVA for that info: (http://www.avahifi.com/root/audio_basics/ab_pdf/ab1989.pdf) Or just buy a unit used, and benefit from it's excellent features. I had one in my system from 1981 to 2004(the only piece I couldn't find an improvement for, until I bought a TacT 2.2Xaaa), and it worked wonderfully. The Alon Exotica Grand Reference system uses the little gem, so you can rest assured the design is far from obsolete.

You may be able to obtain a copy of the manual or formulas from the seller in this auction. He mentions having a copy of the manual. (http://cgi.ebay.com/DAHLQUIST-DQ-LP1-passive-active-crossover_W0QQitemZ230247544266QQihZ013QQcategoryZ14977QQssPageNameZWDVWQQrdZ1QQcmdZViewItem)

Thanks all. As I said I was contemplating changing the input coupling cap on the HF power amp, not a preamp. The peak lights in the amp never light up from bass frequencies so as Nj said yes I too believe the amp responds to the load. I just thought it might be nice to add slope below the HF cross point (2.5K)

ET