Suggestions on a preamplifier project with a "A/V processor loop" option


Does anyone have suggestions for good-sounding DIY preamplifiers which have an option to route the signal from main channels through an external multichannel processor ("processor loop") and then back to the preamplifier? How about a 5.1 preamplifier with no surround sound processing?

All suggestions are welcome.

It wold be nice if the program source selection was implemented with some digital logic circuitry (microcontroller). One could even have nice-looking buttons and leds on the front panel (don't get me wrong, I don't want my possibly high-end grade pre-amp look like a lo-fi christmas tree mini-stereo) - although these leds and buttons don't necessary require digital circuitry inside.

Some other nice features would be digital inputs (requires an internal DAC, of course) and a power supply that works with a 220 V/50 Hz mains voltage.
Can you point to any projects that are possibly available online?

What do you mean by unity gain input? Are you saying that the preamp output for the main channels should be the sum of the selected normal two-channel input and possible front channel input from 5.1 (or whatever) input connectors - without any selection switch needed?

I actually thought about this very idea some time ago, because I fell for Harman/Kardon's Signature 1.0 preamp, which sadly is a little out of my pricerange (check it out, it's cool!!). The project mainly stranded because I'd need a 6 way (or 8-way) volumecontrol for the processo-loop to function as intended and that was hard to come by. If you're interested in seeing what i did find out, let me know and I'll look for it this weekend when I have more time and then mail it to you or post it here.

So, I guess it would be easiest and most convenient to just build an ordinary two-channel preamp, and add a separate unity-gain input for an external surround decoder. Then either the "normal" preamp stereo inputs or the front channel input from the multichannel inputs can be directed to the pre-out main front channel outputs.

The volume setting would be done from the preamplifier when listening to two channel material, and from the external decoder when listening to multichannel amplifier.

Does this make sense?