I don't have the exact setup you are looking for, but these two pictures should suffice to say "yes, it should work"
The can is a 1.5" diameter Gemtech HALO, same diameter as your SDN6 (Shadow Angel is more of an expert on mounting the SDN6 on the ARClight XTL if you have questions specific to the suppressor, but yeah, it will clear the XTL body). You will note that I have one of our new 1 CR123 cell lights installed INSIDE AND BEHIND THE SUPPRESSOR! This was accomplished by using the rearmost set of Light Mount mounting holes (there are four mounting hole positions on the ARClight XTL just for crazy setups like this that people come up with!)
I'll be honest, I was originally going to tell you it wasn't a good idea to mount a light behind the can as I figured you would end up with the upper half of the beam occluded pretty badly, but I'll be damned if when you use the light you only get a bit of a flattening of the top of the light beam when projected on a wall, it actually works quite well even with that big old 1.5" can right in front of it!
To boot, you can see I set up a picatinny mounted vertical grip on a chunk of ARC LOK rail mounted to the underside and ran the pressure switch cable out one of the slots on the back of the ARClight XTL right to the vertical grip.
As for a harris bipod, your best bet is honestly probably a Grip Pod in this kind of equipment heavy setup. That being said, if you want the Harris Bipod, you should be able to just use a #5 Harris adapter dropped right through one of the front underside ARC LOK slots on the XTL and mount the Harris direct, and skip the picatinny altogether. (Sorry, I have a Harris #5 and Harris Bipod somewhere around here, but not quite sure where at the moment.
Also, Merry Xmas to the guys who like to spot new unannounced products in pictures, I didn't feel like removing something just for one picture.
Sven
Manticore Arms