I used to have the Boss RC-20XL. It let you pre record up to 11 loops, which was useful cuz the band played to a metrenome. Otherwise, may be a disaster...
I use a Boss DD-20 in the parallel loop of my F-100. Works fine, but I had to set the DD-20 to +4 Output, turn the effect level to max, and the effect mix on the F-100 to 90%. This setting is a perfect volume mix though, especially for looping.
I have 2 of the 2x12 3/4 back cabs and like them alot. I have found them to have plenty of bass with my F-100 head (Don't know if the F-100 puts out a lot of bass or the cabs handle it better). I prefer them over the Recto cab because I find them to be less directional, meaning I don't have to...
I attended the one in Thousand Oaks on Tuesday night. Very cool night and what a player he is. He makes that LoneStar sing. I noticed that the one pedal he used the most was the BB preamp. It seemed like the other pedals didnt get used more than like twice. Also, he had the Stiletto Clean set...
I have no problems with the DD-20 in the loop of my F-100. That is the only pedal in there, and I am using quality 3 foot cables for send and return. It might be in fact the cables that are actually killing your sound, rather than the DD-20...