It is wise to be patient and methodical in this scenario. Listen and evaluate how the KR amplifiers and preamplifier work together as a pairing. Your P135 preamplifier is very highly thought of and considered to be very good sounding. Using the DHT 45 tubes is an excellent approach and by many accounts, well implemented.
With regard for the Wavac PRT1 preamplifier, is your supposition based upon it’s much more expensive and is better by default? It may or may not be better sounding. Granted it does possess an undeniable intriguing mystique and aesthetic beauty. It’s a circuit based on the 12Au7 tubes and I suspect exceptionally well implemented and has a separate external power supply.
I do not doubt it sounds terrific. But is it necessarily better? Obviously, only a direct component to component comparison will determine that. But I would not underestimate what you currently have. The KR designer is very talented and experienced.
Best wishes
Charles