magnepan mmgs-buy zero autoformers or stands 1st?

Both are excellent ideas to try in your situation. I would suggest first checking with Paul Speltz about the Autoformers. He used to offer a 30 day guarantee, but I don't know if he still does. If he does, that would be the most practical route. If the autoformer doesn't help to your satisfaction, you've haven't lost much on the investment. In the past, I did use both the Autoformers and the Mye stands and both can tighten up the bass significantly. It could be that your tube amps damping factor is too low to get good bass and the autoformers allowing you to use the 8 ohm tap should help.

Tvad is exactly right about the dry sound. That was one of the things I didn't like about the autoformers. Wow. Its been so long I had forgotten about that. Nonetheless, I know quite a few others who are using the autoformers with tube amps with great satisfaction. I think a good bit of the results will depend on how much damping your amp already provides. If you have an amp claiming zero negative feedback, then you may be alright. If your amp utilizes a high degree of feedback, it may sound dry and overdamped.

Cooch: You wrote, "altho, on my reference system i do not get the boominess. that is what puzzles me." I don't know what your reference system is but may well be that the speakers in your reference system synergize better with an amp with low damping factor. Could very well be that the speakers in your reference system are damped in the woofer already (Merlins do this, for example and pair better with low damped amps). The use of little feedback in your amp indicates a low damping factor. Tvad recommended using the Maggies on the 8 ohm taps as this is known as "light loading" and will increase the damping. You may consider calling Magnepan and see what they advise about "light loading". If they tell you "no, don't do it", then don't. The autoformers will transform the impedance allowing you to use the 8 ohm taps and acheive higher damping. In my experience with Maggies, they respond better to amps with high damping factors (as always, there are exceptions). I don't think the break in time with your amp is going to cure the boomy bass; I truly think the boomy bass is directly related to the use of little feedback on the amp. I'd first call Magnepan to see if you can try "light loading". If Magnepan says "no", call Paul Speltz to see if he still offers the trial period with the Zeros. Short of these steps, I cannot think of any other solution other than a different amp. Good luck.