Decided to try a SPU cartridge

I am also an admirer at a distance of the Viv Float tonearms.  I'd probably have bought one already if they were not so costly, and if I did not have some questions regarding the rigidity of the pivot bearing, such as it is.  I have seen them for sale over the counter in Tokyo, at prices well below US prices.  Optional lengths seem to be 7, 9, 11, and 14 inches.  So one way to have high effective mass is to buy the longest one, but that would cause mounting problems on almost any normal turntable (too long), and there is the question of resonance of such a long arm tube.  If you worry a lot about Tracking Angle Error, TAE is much greater with any underhung tonearm than with a comparable typical overhung tonearm with an offset headshell, but my experience with another underhung, the RS Labs RS-A1, suggests one should not be concerned.  The longer the Viv, the less the TAE.  So that's another hypothetical advantage of the longer versions, if you care.  The less the TAE, the lower the skating force generated.  I would not worry about that, either. 

cleeds, I finally found your definition of HTA, which you posted before my post about the difference if any between HTA and Zenith.  Your definition of HTA:

"Your cartridge is in perfect alignment on the horizontal plane when a line drawn between the two contact facets form a straight line pointing at the center of the record."

For a cartridge where the stylus is perfectly cut and mounted on its cantilever and the cantilever is perfectly straight (problems mentioned by Dover) and one of the conventional alignment algorithms is perfectly observed, then the condition you describe occurs twice over the course of playing an LP, at each of the two null points, where Tracking Angle Error = 0.  OK. That makes perfect sense. Now what is our definition of Zenith?  If Zenith = HTA, then it must refer to the orientation of the stylus tip in the groove.  That is not a conventional geometric definition of Zenith. Nor is it an aeronautical definition. (I consulted a close friend who is a pilot.)  That's OK as long as we know what we mean.

I don't think HTA = zenith.  The term HTA is relatively unfamiliar to me but as defined here it is the same as "Tracking Angle Error", the angle by which the cantilever deviates from tangency to the groove, TAE is the term I usually use.  TAE or HTA is changing as the stylus traces the LP and the tonearm rotates on its bearing.  Zenith is relatively constant, if the reference point is the LP surface.  I It changes as the TAE, if the reference is the orientation of the stylus in the groove, but it is not identical to TAE/HTA.  I am not planting a flag here, but it is a good idea if we all speak the same language.  I certainly can be wrong.

A SUT converts voltage into more voltage (Jason), at the expense of current, which is only one reason it would be nonsensical to drive a current driven MC section from a SUT.