I just picked up on this thread today. I haven't been posting on Audiogon for long, but I've been in or around speakers and building for 32 years. A Simple capacitor circuit should not cause any damage to your speakers or amplifier. What you will find is that your panels will swing in impedence at given frequencies and your capacitor will not properly cross your speakers at a given point like your are probably after. If you can get impedence readings, you can put a simple impedence correction circuit in your speaker leads at your speaker to help. This is common and works, but when you say thay you are using panels, I assume that you mean planars, ribbons or electrostatics. Electro statics will not like a cap, planars and ribbons will handle the cap, but correction circuitry will most likely stabilize them at a lower impedence. With all this confusion said, it is a much better idea to go active filters... Unfortunately a poor filter can really contaminate the sound of a good amplifier and a great filter is a lot of money. My best advice is to use your panels full range and adjust your subwoofer to blend or spend the money on a good high pass active filter. Some panels do have some pre made crossovers for passive high pass (maggies). Good luck