[mix4fix]

Maybe they had limited staff and no tech when this REL person gave a bad answer in the reply. 

Bad advise is still bad advice. Are they going to fix your pre-amp if it gets damaged?

[mix4fix]

http://www.faqs.org/faqs/car-audio/part4/

I always refer to this whenever the discussion of combining RCA signals comes up. It's car audio, but it's the same principal. As long as you have that 1/4 watt resister on the center pins, everything is good. I built and still have a summing circuit I built long time ago. I used a radio Shack project box, multi-RCA panel, resisters, and some wire. I had it set up where the two middle pairs were stereo and the two outer pairs were summed. It's weird but I can never miss-connect anything. Stereo in, stereo out, and four mono connections. Plus, I don't like destroying functional RCA cables.

The DIY crowd I know said use 10K ohm resistance or more. There was also a mention of using OP-amps.

https://www.electronics-notes.com/articles/analogue_circuits/operational-amplifier-op-amp/virtual-earth-mixer-summing-amplifier.php

[hilde45]

REL followed up, both with a clarification and the willingness to reach out to my amp manufacturer. And with the offer to talk on the phone, and a phone number.

I think they've been impressive every time I've dealt with them and this is one-off -- and they're sticking it out to make it right.

And also: I bought their product used and still, they're helping.

Full confidence in REL.

[opnly bafld]

REL followed up, both with a clarification and the willingness to reach out to my amp manufacturer. And with the offer to talk on the phone, and a phone number.

I think they've been impressive every time I've dealt with them and this is one-off -- and they're sticking it out to make it right.

And also: I bought their product used and still, they're helping.

Full confidence in REL.

 

[Letitroll98]

Excellent.