I may still try the plugs out of curiousity. Do I need 2 kits, 1 for each speaker? I had them in my cart and it looked like each kit had one of each type of plug? Also, I called hlabs to see if they could send me detailed specs on the high pass filter. Now that you mention that the crossover point can vary depending on impedance, I did notice on the package that it said 60-70hz for the setting I have it on. I was wondering what that meant.
EDIT: I talked to the guy that makes the hp filter and he assured me the impedance of my receivers input would make no difference. The filters resistance is 22k and the receiver is 47k according to the manual. He did say that some tube amps can be all over the place but the average home audio equipment is very compatible and there's nothing to worry about if you're not using professional grade equipment or weirdly spec'd tube equipment. I can honestly say from my own experience in the last hour and a half of using the thing at 70hz that it sounds significantly better than 80hz in most ways. 80hz crossover had less boom in the corner but the sierras had a lot more to give between 70 and 80hz and now sound more fleshed out and natural. Unless I misunderstand the frequency response graphs for the sierras on this site, the natural crossover point is 70hz or so since this is the -3db point correct?