As posted in another thread, I met Bob's son in college and spent a fair amount of time with him and his dad. Also played at Romine's and was around Terry Sr. (former co-owner and now owner) and Jr. for 15 years. Bob pronounced it as "Shawn", said it meant beautiful in German, never really heard "Shown" being said much at all until I traveled, in various spots around the country I've heard both "Shown" and "Shawn" very commonly used with confirmed advocates in both camps for various reasons.
I've seen posts by several language "experts" (some of whom are probably right) about the several different meanings in the native language, the affect of the umlaut on both pronunciation and meaning, parallels with other Nordic-type languages, etc. That's all good information, but it should be pronounced the way the owner of the company pronounced it, linguistically correct or not, don't you think? After all, for these purposes it's a brand name not just a word from a language.
Scott