Mdrconsult,

I am a former owner of a Model 990 but current owner of two Yaqin single twin triode tube buffers and one Musical Fidelity X10v3 tube buffer. I used all of them in a 5.1 home theater system with my 990. If you are purchasing a Yaqin tube buffer, make sure to purchase the Pacific Valve and Electric Company version. This one uses a single 6922/6DJ8 tube vs. the Yaqin twin 6J1 tubes found on eBay or Grant Fidelity. There are many 6922/6DJ8 variants that the 6J1 tubes just doesn't have. You will find that the Yaqin when using the right tube in your system will sound better than the MF tube buffer. Will there be a disparity if you only use one Yaqin just for the front mains. Probably depends on the resolving power of your home theater system. I use Magnepan IIIa for front and rears. So I can definitely hear the timber and warmth differences with and without the Yaqin in place. Maybe your ears won't be as critical and try out one before purchasing another. Don't waste your time adding your subwoofer to the tube buffer, it actually muddies the bass on my Velodyne HGS-12. You probably can get away from purchasing a third Yaqin just for the center channel just because the center channel will not be the same as the front or rear speakers that you use as in my case. So there are already compromises. In terms of warm up, the Yaqins actually only need about 10-15 seconds to fully warm up while the Musical Fidelity needs close to 30 seconds. But you will find that everything will stabilize within one minute. Also, I shut off my Yaqins when not in use. It will increase their life expectacy for the tubes. Hope this answers your questions.

Slbenz