I haven't read the HEALTH section yet!!!
If you haven't tried this yet, IMHO I'd try a 30 day course of tetracycline and keep him on the LR during this time.
Kelly was in remission for about 20 months before we did the switch. But he's been doing very good on the diet. He's currently getting the kibble as mentioned above along with either 1/5 to 1/6 can of EVO 95% canned beef or 1/2 can A/D that he splits with Ringer. He's eating leftovers, treats from fast food restaurants, and on his birthday on the 12th he had a bowl of ice cream. He's gained almost 7 pounds since he went back on a regular diet.
Unfortunately he had a bone biopsy Tuesday and isn't doing well right now. The biopsy was in his right front leg, but he's having problems with his rear end now. He only started to drink water this AM and he hasn't eaten anything since Monday evening. He went back to the vet yesterday for SQ hydration and pain shot and I'm taking him back tomorrow - but this has nothing to do with his SIBO.
GOOD LUCK with whatever you decide to do!!!