I've narrowed it down to the Minus K (BM-8, not the low profile model), Stacore Basic and the Vibraplane. There is a favorable lengthy discussion of the Stacore on WBF and Stacore also states that their platforms are truly intended for music (while the Minus K may not?). Vibraplane is a tested product and although passive, is similar in price to the Minus K (~US$3200). The Stacore Basic (also passive) seems like a better built Vibraplane, but also is higher in price (retail $5k). I've heard in general that the Minus K may be fussy for optimal performance, but mostly from non-owners - it has the best specs (theoretical) for performance. Would really like to hear from Minus K owners.
Frankly, I could probably live with either of these three and it's likely going to come down to economics.
Frankly, I could probably live with either of these three and it's likely going to come down to economics.