I don't know about the MRS, but when I tried to plug my poratable (running on AC) to
my VM3100Pro (connceted to my stand-alone computer via the StudioPak (RPC-1), I got a terrible disk/mouse activity noise, which was ONLY stopped by a ground lift (On a direct box) - the DI box didn't help unless it had a ground lift.
Luckily, there is company that makes this device - Whirlwind maikes the pcDI I used two adapters to go from the balanced output back to rca. The ground had to be lifted - the other functions of the DI box were irrelevant. For full stereo I/O I'd need two of them, but I'm only monitoring the output thru the VM , so one is enough for me...........
I had the same problem with a Mackie, but no other equipmen, so I'm suspecting the VM might not be grounded correctly, but who knows.... In any case, the pcDI solved the problem...
(You can find out if it is a ground loop by cutting off the third prong of a Radio Shack adapter, but this is NOT, repeat NOT recommended as anything but a reality check - pulling the ground of AC (rather than the signal) is very dangerous to both you and the equipment if lightning should strike...........
Just my input - if there is a buzz, it probably isn't the MRS, but a ground loop, as above..... chasing them down can be a real pain in the .........
Best Regards,
Chuck
bunnygirl said:
clansfolk- i did notice a buzz using the guitar input on the MRS with my tak but thought that it was my tak pic up or cable. when everything is plugged in and i squeeze the TRS connector that is going into the guitar (it's an acoustic electric) the noise disappears. let go of the cable at the connector and it returns. it's it's actually loud noise, not some little cable hum. sometime this week i'll plug in my martin A/E and see if it does the same thing and update you. maybe a DI is all that is needed. is that why when I hold the connector, my hand acts as the ground for the unbalanced line? why is there so much NOISE going through to begin with.. hmmm. anyone one else have similar probs? 
-curious bunny girl