I have a Radial Workhorse Powerstrip for my 500 series modules. On the back, there are both XLR and TRS ins and outs for the units. One of my pres, the Chandler Little Devil, has the ability of accepting line level as well as mic/DI level. My question is, would it be bad to have cables running to both the XLR and TRS inputs simultaneously? I would by no means intend to have signal feeding the pre from both places at the same time. I'm just wondering if that causes an issue. The question could be stated regarding any pre with two inputs like this. I would like to have the option of running a line out from my interface into the pre in case I want to color an already recorded signal. I'd rather not have to start plugging and unplugging things to do so. If it were possible to have both the XLR and TRS ends plugged in simultaneously without issue, that'd be great.

From what I can tell, the XLR and TRS jacks are hardwired together which gives you the option to use either. If you use both this would be effectively the same as if you used a Y cable. As long as both sources weren't very low impedance I don't believe you would have any issue doing this if you needed to. I see no harm in trying and see if you can hear any audible difference.

I'm not really seeing the musical benefit of doing this though ... what are you trying to achieve? Running say two mics into one mic pre would give you no opportunity to balance them or resolve phase issues or whatever ...

I'm not trying to run two mics simultaneously. As I mentioned in my initial post, one of my pres has the option of switching to a line level input as opposed to a mic level input. Since the Chandler Little Devil can be a very colored pre depending on your settings, I would like to have the option of using it as a hardware insert in Pro Tools so that I can run a line level signal through it for color/distortion/whatever without unplugging the XLR connection I have running from an XLR patchbay where I plug mics in during recording. The rear of my rack isn't the most accessible thing in the world, so I'd like to avoid going back there to change up the cables if I don't need to.

Fair enough. As far as I can tell, that would mean you have a microphone connected across the input to the XLR while you are using the TRS input to process your line level stuff? Frankly, that doesn't sound like a good idea - even with the phantom power switched off it would be a load on the input, and possibly a source of noise.

I could be wrong, but I would not do this. I would use a patch bay, or at the very least run some cables so that the XLRs are where I can swap them.

Straight newbie here , I have an Art Pro MPA II 2 channel preamp into a WA76 single channel compressor. I wondering can i plug channel one of the preamp by xlr into xlr input of the compressor and channel two of the the preamp into the trs input of the compressor. And just mute the channel im not using. Will this cause any issues?

I just posted this in another thread:
It's not easy to sum two outputs into one input.
This old Rane Note explains it.

Why Not Wye?
Dennis Bohn, Rane Corporation
RaneNote 109 written 1991; last revised 4/04

Splitting Signals
Subwoofing in Mono
Unbalanced Summing
Balanced Summing
Output Impedances

Introduction
Wye-connectors (or "Y"-connectors, if you prefer) should never have been created.

https://www.ranecommercial.com/kb_ar...p?article=2106