Before sharing what I have been doing, I have to remind anyone reading that the most widely accepted set up follows the Petzl recommendations:
and I certainly would suggest anyone to pay attention to their recommendations, considering what follows just what someone online without any authority in the matter has been doing for a few years now.
I use two strands of a static rope, tied at the anchor via two independent locking biners and a double figure-8-bunny-ears knot - one biner for each "earlobe" tied to a different bolted anchor, or sling around a tree, as the situation presents itself.
I use both strands tied to my harness loop via a locking biner and two side-to-side Micro Traxion devices. After coming across this post showing how twist-lock gates can be opened by the rope, I changed the configuration in the picture to a screw-gate pear-shaped locking carabiner:
Old method (self-locking biner with two MicroTrax's):
New method (screw-gate locking biner with two Micro Traxion's):
Cross-loading the biner has never been an issue for me, but it required some adjustments at times, so I am more recently using a Climbing Technology Concept SGL with an ACL system to prevent this issue:
In addition, I have incorporated a clove hitch on a locking biner to one of the strands of static rope below me (see second image above). As I climb, I periodically slide up the clove hitch without unclipping the biner, simply by pulling up on that strand and sliding the rope. In this way I keep the extra safety of the clove hitch on the biner relatively close to me. Its function would be to act as the ultimate safety if both Micro Taxion devices were to strip the rope on a fall, or failed for other reasons.
At the bottom of the crag, I used to tie the ends of the rope to my backpack through a single clove hitch tied with both strands and secured through a biner to passively help with the sliding up of the Micro Traxion devices as I climb:
However I abandoned this system because the weight of the rope tends to be enough to make the MicroTs slide as I climb above some 20 feet off the ground, and having the backpack tied to the end used to be a constant source of annoyance.
The two-strand setup offers redundancy, but also allows the Micro Traxion devices to stay parallel to each other, as opposed to in line as in here. I find that having the Micro Traxion's one after the other on a single rope wedges them together splaying the orange casing of the top one.
If I need to ascend and top-off, or descend from a point without support I use a Jumar (*) to disengage the MicroTraxion's (impossible under weight).
However, and as an alternative, one of the strands of the rope will come handy in releasing the tension in the system: I can tie an alpine butterfly knot on the strand that will not be used to descend to provide me with a way of placing a foot through it and stepping up on it to release all tension on the harness loop at which point I simply open the biner, leaving the Micro Traxion devices on the rope until I have all my weight on the descending device (usually a GriGri, or Munter knot as an alternative). This is the picture of the alpine hitch on the non-descending strand ready to step on:
Naturally, before I disengage the Micro Traxion's I already have a GriGri or a Munter knot set up on the descending strand. The GriGri is most efficient, and easy on the climber and the rope, but I want to illustrate the Munter since it is the back-up system when the GriGri is dropped by mistake during the setup process. Here is a quick home-made video of the tying up of the Munter knot before disengaging the Micro Traxion's. This is the picture of the Munter before backing it up:
Typically, the Munter is backed-up with a mule hitch and an overhand knot:
Here is an image from this great animated illustration of the Munter with a mule hitch back-up by knots by Grog of what the steps are (Munter, mule, backup half-hitch):
I tie up the Munter a bit differently (as on the link above) because it makes it easier to set up the Munter ready for rappel (braking end away from the gate). Here is the entire process of setting up the Munter-Mule with a clove hitch as a back-up, and the alpine butterfly to relieve weight of the Micro Traxion's.
After I release the Micro Traxion's, I hold on tight to the loop in the mule hitch and compress from top to bottom the Munter to keep it from sliding down. It is important to watch for cross-loading on the biner, and try to get the loops of the Munter along the basket of the biner parallel to each other.
In addition, I do tie a second clove hitch lower down from the Munter on the descending strand of the rope, fastened to the loop of my harness (tied below the HMS biner for the Munter with a self locking biner), which I disengage only when the Munter is already in rappel mode (i.e. after untying the overhand and the mule hitch). The clove hitch is more often than not the only "back-up" for the Munter (in lieu of the mule).
Before unfastening the overhand knot and the mule hitch from the Munter, I make sure to adjust this back-up clove hitch so that it is at some distance from the Munter in case this slides down a bit while disengaging.
(*) Carrying a Jumar is always a good idea, because the way out of a situation may be climbing up, rather than lowering oneself. In the absence of a Jumar, this can be done with two Prusik knots.