With the Atma-Sphere S-30 the front row of 6SN7 tubes will have the most influence on the sound. I use Raytheon VT-231 tubes in this position. You could also experiment with the back row of tubes as well, but to me it is a less significant influence on the sound. That said I use Sylvania 6SN7 GTB tubes in this position. Depending on my mood I leave the Chinese tubes in the middle row or I use shorting plugs that Ralph made for me in place of the tubes. The shorting plugs drop the gain of the amp 12 dB. To me this makes the biggest difference in the performance of the amp in my system.
The amp is very transparent and should match up well with your Quads. As for your preamp, Ralph has indicated many times that the most difficult role for the preamp to fulfill is to control the interconnect. Does your preamp support the 600 ohm standard for balanced operation? If so, then you should not be able to hear any difference swapping interconnects between the preamp and amp.
As others have mentioned speak to Ralph. He is extremely helpful in matters such as this. Personally I don't think cables are the solution.
The amp is very transparent and should match up well with your Quads. As for your preamp, Ralph has indicated many times that the most difficult role for the preamp to fulfill is to control the interconnect. Does your preamp support the 600 ohm standard for balanced operation? If so, then you should not be able to hear any difference swapping interconnects between the preamp and amp.
As others have mentioned speak to Ralph. He is extremely helpful in matters such as this. Personally I don't think cables are the solution.