I also have a Threshold Fet 10e and S350e power amp. I briefly had my system bi amped with a loaner amp " Threshold 400a" I didn't have balanced cable at the time and just used a RCA spliter connector and the Fet 10e seemed to drive both amps fine. I am currently just using the single amp "S350e" with a pure silver balanced XLR interconnect "Signal Cable Silver Resoslution". I would most definately recommend the balanced cable on the amp driving the top end, midrange and tweeter. I found the sound to be much more open, smoother and transparent with better detail using the balanced connection. I have tried to contact Jon Soderberg also with NO success. What's up with that? I was considering getting a sub woofer and driving it off my umbalanced pre output but when I called Threshold about it a guy told me that the Fet 10e was only meant to use one output, either the balanced OR the unbalanced but NOT both. Personaly I think the Fet 10e IS up to the task as I did drive two amps with it before just as you have and feel that it should also be able to handle a subwoofer amp also. One thing I find strange about using the balanced XLR connection is that they say there should be a 6db increase in gain due to the balanced connection BUT for some reason I seem to be noticing a slight LOSS in gain with the Threshold equipment. The sound is great but it seems like I have to turn it up a couple of notches louder than before. I was trying to contact Jon about this but no luck. Hope this helps, if you have anymore questions or just want to chat Threshold, feel free to email me.
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