What's the purpose of a preamp?

[Firebottle]

Well, what kind of budget would make sense, in order to substitute my current Croft Micro 25RS LS and get a significantly better performance?

Thanks

I would stick with your Croft 25. The problem with a stand alone passive attenuator, even the Khozmo, is that it softens the transients in the music. How audible, or not, is totally dependent on the synergy with the interconnects and power amp.

The best way to implement a passive attenuator is to have a zero gain buffer immediately after the attenuator, I have heard of the improvement this makes with a Khozmo pot.
I am working on a lower cost unit using this approach.