I saw some info here on a tube buffer stage Gary Dodd is making now. Perhaps looking into it might solve your situation. he is also proposing a HP amp as well. The Dodd audio web site should inform you more. Both items run around a grand a piece, depending...
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I took a look at the manual for it, which also includes some specs on the last page. It will certainly function in the manner that you describe, but whether or not it will provide any benefit is questionable.
I note also that there is no spec on output impedance, output level, or gain for the preamp outputs. And it is a bit worrisome that it says that the preamp outputs can be connected to the "audio input on your integrated amplifier, preamplifier, or receiver," but does not mention the possibility of connecting directly to a power amplifier (although I realize that is not your intention). That leads me to suspect that its gain is low and/or its output impedance is high.
If you decide to pursue it any further, you should probably ask the manufacturer if they can provide these additional specs.