As other people have said, it's essentially impossible to get high on bupe if you're already taking 8 mg/day.
I was prescribed Suboxone when it first got on the market and my doctor put me on 24 mg per day. Ridiculous. For years, before I understood how bupe worked, I tinkered endlessly with doses of tagamet, cimetidine, diphenhydramine, and benzos in attempt to "feel my dose more". It never worked. I felt more sedated when I took benzos or benadryl, because they are sedatives. I've taken 48 mg of bupe with absolutely no effect. Using mouthwash to increase bioavailability will do fuck all for someone on large maintenance doses - the problem isn't bioavailability, its the nature of bupe. Your system is chock full of bupe already.
Over the years and several sub docs later I finally came to realize than less is MUCH more with Suboxone. Once you get below 2 mg per day, not only will you feel your doses more, there will be less in the way of side effects. And if you're like me, doing the weekend warrior thing, taking days off the sub to use your DOC, you won't have to worry about its blockade effects.
I've found there was absolutely no benefit to taking more than 4 mg per day, and i felt best at about 2 mg. But sub maintenance did nothing to curb my cravings, like you i was still trying to catch a buzz and all it did was keep me from being dopesick between doses of heroin and oxy. I ended up on methadone maintenance which is a special kind of hell but at least it curbed my cravings and anxiety.