I currently own 2 T400 amps. I paid $2,000 for each in mint condition. You need to be careful matching the pre-amp to the T400 if you are going to use balanced mode (recommended). The T400 requires a very low impedance output (less than 100 ohms) from your pre-amp in balanced mode.
I tried to match them with a Sonic Frontiers Line 2 Tube pre-amp with no luck for that same reason. I matched them witha Threhsold T2 pre-amp and they sound great! I also sent the T2 to John Soderberg (Vintange amp repair) to be modified and it sounds even better. You can pick up a T2 for about $1850.
I hope this help you.
I tried to match them with a Sonic Frontiers Line 2 Tube pre-amp with no luck for that same reason. I matched them witha Threhsold T2 pre-amp and they sound great! I also sent the T2 to John Soderberg (Vintange amp repair) to be modified and it sounds even better. You can pick up a T2 for about $1850.
I hope this help you.