I'll be honest Shawn, I have 4 tangs in my 240 and they are a bit scrappy..... you are looking at 6..... all more or less teh same size and shape.... it could be disasterous..... I personally wouldn't do it.
Similarly, I wouldn't do teh trio of yellow tangs either. I had 5 in my 240, they bickered and scrapped all day long, constantly looknig tatty..... its stressful for the fish, and just not right, IMO. You can do it, but just because you can it doesn;t mean you should.
My advice, for what it is worth, and I think you will be more please in the long run anyway, would be to scrap the tio of yellows and the sohal and naso, and get a single yellow, a purple tang, sailfin tang, regal tang and your existing kole tang. To be heonst, at that rate, I still think your pusing it, but it is more do-able than the other propositions.
Again, personal opinion - but I wouldn't bother with a trio of yellows anyway - they won't school and be buddies, as I suspect you hope - they chance meetings where they group of coincidentally, for a few seconds at a time......
Adding a regal angel - well i would ask, are you fully aware of the delicate nature of this species? A 210 tank, with 5 tangs and an established coral beauty might be a bit rough and tumble for a regal angel..... but if you are aware of all the pit falls, then go for it - though I wouldn't give you very good odds. I would prehaps go for a majestic instead - relatively, they are quite reef safe, and is all but gauranteed safe with sps..... much hardier, more outgoing, and a much better choice all round, in my view..... emporer angels have a good track record, realtively, with sps also.
HTH - all just my opinions of course

Matt