Hi there cjc,
I'm gonna suggest something that may or may not take care of your problems. This advice is what I found works best for me, and maybe the same will apply to you as well...........who knows.
I've found that no matter how good my prep, lather, and technique is, there are some razors that will just not give me a comfortable shave. Most superspeeds are like that for some reason, plus other more aggressive razors have the same result. It's only by trying many razors over the years that I found out what's up.
After two months your lather and technique should be pretty darn good. You should be getting consistantly close and comfortable shaves at this point. If not, then I'd consider trying a razor like a Tech or a Gillette adjustable set on a low number(like3). The good news is that you have lots of experience now, and should notice a difference right away when using a new razor.
Maybe buy or ask to borrow one of those two types, and see if that doesn't take care of any issues. I've never used the Merkur you own, but have heard it's a little on the aggressive side. This may be the cause of irritation if your face isn't suited for that.
Heh, this 'hobby' does take some tweaking to get right, but don't be discouraged. The rewards are worth the time and effort.
I can quit at any time that I decide to. Unfortunately, I have NO control over when (if ever) that decision might occur.