My concern with swapping out the preamp is that I love how the basses sound already, whether the LH3 colors the tone or not. I don't want to change it.Well personally I would check into a Glockenklang preamp or a Nordy preamp... those both use a five knob layout and would drop right into your 44 or 55 series basses you own. If you want a super clean preamp that doesn't color your tone up the Glockenklang is the ticket. I had one in a five string Human Base I used to own and it was a very clean and transparent sounding. The Nordy on the other hand IMO is not... it's a mixture of the old and new school sounds without going too far either way, great preamp though, my buddy down the street has a Callowhill five string Junk bass with one in it and Fat Stacks, it's one heck of a bass!
Peace,
I've also thought about just putting the treble control in the cavity, and putting a PTC in it's place. I never boost treble, so I'd just set it flat, wrap it in a little foam and tuck it away inside. A PTC would be all I would need for controlling top end when I want to darken things up, especially on the fretless.

