Funny you should mention that.

I hooked up my M13 to my DT50 just last week and connected it thus:

JTV69 via 1/4 inch to Dunlop Crybaby, MXR Dist 3 to amp input.

I connected up the M13 into the FX loop of the amp.

I had a L6 EX1 pedal plugged into the M13 to deliver a boost on the tube compressor model.

Only had Vintage Chorus, Dynamic Delay and Cavernous reverb rounding out the bottom row of switches. Kept it very simple.

The only other unit is a single button channel switcher to switch between Clean and Mesa for the amp.

Answer: Completely frickin useless

On both occassions within a week I took it to two different jam sessions so couldn't blame the electrics. I thought my amp had fried, died and plain dumbfounded me. When I used my pedal board with just analogue pedals no problems at all. Note, the mix knob on the amp FX return is always set straight up 12 oclock no matter which system I use.

The problem was sheer lack of balls and volume from either channel. The master volume was on max and both channel volumes around 2 oclock. Now this would have blown the windows out with my pedal board. The boost available from the EX1 pedal was just plain wrong for amp channel 2 and produced all manner of crap. I seriously thought my output valves had died. I tried swapping out all cables and even went direct to amp, but whatever was going on effected my amp big style until I switched it off completely and went direct from guitar to amp input and normal service would resume.

So after giving up trying to make this very simple config work I tried out the HD500 and L6 Link and nearly tore the doors off the garage as I had forgotten to turn down the master volume. I had programmed the HD500 to mimic more or less exactly the same as my analogue pedal board and indeed the M13.

JTV to Wah to MXR Dist 3 to input of HD500. Pedal on the HD500 only controlling a compressor gain boost from heel to toe which gives a subtle but very effective variable solo boost permanently engaged on both patches.

Loop of HD engaged at the end of the chain adding an external EQ pedal then Ernie Ball Volume Pedal for instant off. No effects whatsoever before the Pre model amps in the HD500 so post pre amp chorus, delay and reverb sit presumably in the DT50's effects loop as to my understanding. Now this system works and all I have are two patches. One to select the clean channel of the amp Topology 1 and patch two to select Topology 4 Mesa. They more or less sound just like the amp does if I plug a guitar lead right into the front of the amp although not exactly the same. (Discussed elsewhere on the boards). I'll live with the downside of slight loss of tone/feel for the flexibility of using my own pedals and just the effects of the HD500.

I tried some months ago using the M13 in the 4 cable method but no matter which bypass mode was selected neither yielded an ideal solution unless I was willing to have at least one unit engaged at any one time otherwise there was a serious loss of signal. So I chose to use up the last slot on the M13 with a reverb and turn the reverb off on the amp. That only left 3 available effects slots which isn't exactly ideal. There was also a fair amount of electrical noise which I could not remedy completely but was lessened by putting the M13 power supply at the furthest distance I could from the rest of the gear. Needless to say I gave up on the M13. I will say however, that I have tested the M13 in front of an amp and it works just fine.

It's a wonder I have hair. It's for some of the reasons mentioned above that I went back to analogue pedals.

Good luck dude