Well I drilled some holes and wired up the new RCA's on the back of my amp, so now I can switch between direct input (bypassing the preamp) and the normal integrated path. Works nicely and I suspect that the slightly soft top end was actually due to the preamp as the sound seems a bit crisper now on the direct input.
However.... when I switch from direct to via the preamp, or vice versa I get a big thump from the speakers
I can avoid if I switch the speakers off but it is not particularly family friendly, especially since I have a 21 month old who will love to switch the switch on and off
So I'm not sure if it is switch contact bounce or perhaps just switch on thump (the fact that there is no thump at all when switching to the off position leads me to belive it is more like a switch on thump), but it is rather anoying. Puts a bit of a damper on an otherwise successful mod. The switch is a center off type, I might have to get a three pole...