Already have both boards set up in the studio side by side.Did hook it to the M-3700 today to test it after transporting to my studio everything worked perfect.Have noticed that the M-2600 is alot quiter than the M-3700
After years of using the M3700 I have found the following.
The noise on the stereo outs is greatly reduced if you mute all the Aux sends and the Monitor sends, only un-muting the ones you need to use of course.
Depending on the outboard gear connected, monitor amps, recorders, etc, running an external earthing cable between chassis of the gear can reduce earth hum massively, this is trial and error.
You may also have to lift the earth on audio cables going to monitor amps. Also don't forget that the M3700 has pin 3 hot on the XLR outs so if you have pin 2 hot on the amps you may need to make a phase reverse cable if there are problems.
Due to the fact you have automation on a M3700, by programming unused channels to turn off when there is no signal present makes a very quiet mix.
If connecting a computer interface to the stereo record outs and 2track in, use a signal isolating transformer inline (both outputs and inputs) reduced digital noise to 0.
And finally, you are recording in the analog world, don't be afraid of the Red, use a strong gains on the inputs and to tape and this reduces the noise floor, and gives that analog sound.
My M3700 is near silent on mixdown, the metering on the computer is barley off the 0 with no signal, a reasonable mount of channels open and the stereo outs turned up. It's funny, every now and them I think I have a bit too much noise, then I hit play and realise that I have the monitor volume right up and blow everyone out of the room.
Cheers
Alan.