Vibraplane was something that I looked at initially as well and it seems that ebay is the best source. The price is right but there is not a lot of information about it. Most sellers only shipped within the US and some will only sell it as is with no guarantee that it is actually functioning :(
I am also worried about servicing if the unit has a problem overhere! So Minus K seems like a safer choice for now.
I think that using separate platform on top of Minus K will also allow for easier centering of the mass rather than using a larger custom top. I am a bit worry about using aluminium as top plate as well. In the past, I experimented a bit with aircraft grade aluminium platform under speakers, turntable, amps etc. I find it to give better impact, more focus bass, extended top but at a cost of adding hardness and edge to midrange. Of what I could find locally here for TW, I find black granite (one of those with higher density than regular granite) to be better than local pooltable slate slab and both better than aluminium by a bit. I wonder what would be a good footer for the slab of slate/granite on Minus K since there is a little screws on top on K Minus so I can't lay a platform on top directly.