I'm hoping someone can help me with using stompbox effects pedals through the external effects loop of a multi-effects rack preamp (in this case, the Digitech GSP-2101 Studio Tube preamp processor). I have an existing patch that absolutely NAILS the EVH "brown sound", and I attempted to use my MXR flanger with the patch for playing "Unchained".

I chained the pedal through the effects loop and changed the external loop setting within the patch to "no sum" (as per owners manual). The patch recognized the flanger pedal, however, switching the loop setting to "no sum" (whether pedal is on or off) changes the sound of the patch...it becomes somewhat weaker and thinner sounding (it did this with every patch I tried)...and the MXR flanger is almost inaudible, like its buried in the mix. The patch does NOT recognize the effects loop unless the "no sum" is chosen.

Unhappy and frustrated, I decided to run the flanger through the front input...and it sounded FANTASTIC (at least for the over-the-top flange sound on Unchained)!! However, I was ALWAYS told that you should run your time-based effects pedals in the FX loop, and never in front of a preamp (especially high-gain). It just seems I shouldn't have to do this when there is an effects loop to be utilized. not to mention the unsightly cable now running from my pedals to the front of the GSP.

Am I doing something wrong? Are there settings I need to adjust in the patch so it utilizes the effects loop better...or does the GSP-2101's external effects loop just SUCK BALLS? Unfortunately, Digitech no longer provides support for this 18-year-old processor, so I was hoping someone here may know.

Any assistance is GREATLY appreciated.
I believe you may need to increase the send/receive levels of the effects loop.
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I dont see an option ANYWHERE to adjust the "send/receive levels of the effects loop", but I did come across this in the manual...

NOTE: External devices should return the same signal level to the GSP-2101 as they receive from the GSP-2101. This will avoid level changes when switching the effects loop in and out. This signal level relationship is called unity gain.

I just wonder if the MXR is incapable of returning the same signal level, and if that's the case, would adding a boost pedal before or after the MXR help??