I can't speak for your "6x6", but I shoot Minolta 35mm and Mamiya C330 and have done quite a bit of 'macro'...
With the TLR, you can do some great work with a 65 or 80mm lens. The problem I always had was the parallax correction. I didn't have the Paramender at the time. I used to fram the shot, then swing the camera up to match the needle in the viewfinder. Framing was always correct, but the angle of view changed... The Paramender takes care of that and works great, but adds another step...
With a Minolta 35, I can whole heartedly reccommend the bellows I system with the special bellows lens and focuser attachment. Way back when, I used rings. Dave is completely right. The auto-exposure is great and after a while you just know which ring or combo to use. But the bellows system is infinitely adjustable for magnification and focus. With a meter in the camera like my XK's, I set the stop and the camera simply adjusts the shutter speed. Half-manual ;-)
Minolta made two lenses for the bellows system. A 100mm and a 50mm. They have no internal focusing and they're shorter than normal lenses. You can't use them without the bellows. If you want sharp, you won't find better! I believe a later bellows system may have had the auto arperture ring/cable but I didn't keep up? Maybe the Bellows III?
I also never kept up on "macro lenses". But all the ones I've ever seen are more like zoom lenses that allow you to focus closer than 'normal'. Not what I would consider a macro lens. And way too many elements and movements to be sharp. On the other hand, there probably are some true 'macro' lenses out there that I don't know about, similar to the LF macros that are simply designed for close-up work? They would probably also be good.
From what I know now, with a manual Minolta system, I would still opt for the Bellows I system with the 100mm lens. And one of these days I'll pick up the 50mm to go with it. That's what I consider 'macro'!