Pre-amp for K5881

[Mikehe]

I have build the K5881 in 1994 and updated it to MKII a couple of years later. The speakers are from Focal kit 544 series II.
Finding the right pre-amp has not been easy. I have tried different systems at the end use an audio attenuator CT1 from the company Danish Audio Connect. Danish Audio Connect recommend using a low impedance value of 10kOhm linear.
Because the K5881 is so sensible I have to divide the input signal by 20. Using a 20kOhm to 1kOhm resistance.
It works but the result was never so nice, recently I had the opportunity to connect my loudspeakers to a nice Quad II amplifier, the result was amazing, this motivate me to bring the K5881 to a better result.
I wonder what pre-amp or sensitivity reduction other users have :
[*]I read in the forum that replacing the valves 7025 by 5751 will reduce a little bit the gain, would you recommend this?[*]What resistance value would you use for the potential divider?[*]It seems strange to fist divide the input signal by 20 just before amplifying it, would you recommend a modification of the circuit?[*]A suggestion for a pre-amp maybe?