Any NHT Classic Four owners biamping?

I have found myself in possesion of two amplifiers in the course of my audio equipment buying so I thought I would try bi amping my NHT Classic Four speakers.

Any other Four owners out there biamping? Are you using any active crossovers (like the NHT X2) before the amp? If so, what crossover frequency are you using?

My friend who owns a pair of classic 4 and runs them with two Rotel RB 970BX amplifiers with great results. Since both amps are in exactly the same. He uses one stereo amp for each speaker. One channel runs the lows and the other channel runs the highs. They sounds better than I could ever imagine for a $2000.00 set of speakers . He uses the stock designed passive crossovers which I modified. The crossovers are now set up with sonicaps, Alphacore 12 awg copper foil inductors, Cardas speaker connectors and better internal wiring. I also replaced the dome tweeters and super tweeters with a new set of Aurum Cantus 2GSIs ribbon tweeters. This also required the removal of super tweeter crossover frequency point. This really made the highs much better. The highs extend way up, and now sound natural and much faster. It was a crazy mod but it made this a world class speaker system. I had to use several resistors to get the new tweeters to blend. I had a machinist machine new faces out of billet aluminum for the Aurum Cantus Ribbon Tweeters so that they would fit in the stock factory NHT holes. I also lined the insides with Dynamat, and had better stands made out of steel, filled sand. It is crazy good. In fact I am going to build my self a set sometime this summer.
I was shocked when I hooked the modified Classic 4s up to my Pass Labs X350.5 before I delivered the speakers to my friend. Difference is they now disappear. They have such a natural tonal balance. The timing is perfect. The sound stage is deep and wide. They sure make my audio friend's shake their heads in disbelief. The moded classic 4s had a much better sound than a set of Focal Utopia Divas. The only speakers in my system that sounded better was my highly modified set of Apogee Duettas and a stock set of B&W 802Ds.
Cool thanks for the response. The tweeter mod is a little more than I want to tackle right now, but I would consider upgrading the crossovers. DO you have a parts list of what you used?

I keep meaning to pop the back off and take a look at the crossovers. Did the stock crossovers use decent components?

They did not use good components. You will have to take out all the drivers to get to all the crossover parts. I will get you a list of all the values. Just use the original printed circuit boards just soldier on the better parts on and do replace the intrernal wiring. These speakers are a decent design with a great cabinet, decent midrange and woofer. NHT could have had a Giant killer at $4000.00 and would selling them like hotcakes if they would put in a little more effort.
Thanks. A list of what you used would be great. What did you replace the internal wiring with?

I was thinking of removing the subwoofer crossover (really just a low pass filter) after I biamp since I will be using a low pass filter on the amp input.