In order to really get all you can out of the amp you do need a balanced preamp as you've already surmised. But what most people don't realize is that there is a balanced standard; and that this standard is there to prevent ground loops and also prevent your interconnect cables from imposing a sonic fingerprint. If you've ever auditioned cables to see which is better then you know what I mean.
So I would always check with the manufacturer to see if the preamp supports the standard. Most tube and many solid state preamps don't. This is why there is a controversy about balanced line; there would be none if all the gear supported the standard.
in the other hand I am afffraid to lose openness, dynamic and holographic sound I have with K-1xe preamp.
If would expect this to be improved by a tube preamp.
