Use two per channel in the VTV Amplifier Custom Input Buffer (tube or solid state).

The measured specs are outstanding but the real power of this Class A design is the warm and detailed sound with the Pro SS2590 providing a faithful, accurate reproduction without harshness from IC based OPAMPS.   The following is from the SPARKOS LABS website:

IC op amps are dead. And we killed them.

Op amps are a key component for processing and amplifying audio signals. They can be found in virtually all audio gear in the form of tiny integrated circuits (IC’s) like the one laying on its back in the picture. They also come with all of the pitfalls and shortcomings that IC op amps have, like limited power dissapation and crummy compensation capacitors.  Discrete op amps do not have these limitations, and are a vastly superior  upgrade over their IC counterparts.  They can run much higher power, have much deeper class A bias, and deliver a much more realistic and detailed sound.  Discrete op amps also permit the use of high quality compensation capacitors, and allow for two pole compensation schemes which are impossible to implement in IC designs.  All of this translates into a more detailed and engaging listening experience with better imaging and soundstaging than IC op amps can deliver.