I truly enjoyed my Linn sound, but I am now being drawn to a more neutral/open sound, ....Xagwell,
I love the big soundstage with slam as well.
It sounds like you want it all! ;-)
As between ZYX and Shelter, the ZYX lineup is more neutral and open. Neutrality and seamlessness are the first things everyone notices when they first hear one, and that impression does not fade with time. No colorations, no bloat, no artificial blooming of notes.
The ZYX soundstage has more depth, width and perceivable dimensions. ZYX's also image better than Shelters. This is partly due to their more modern stylus profile and partly due to the excellent channel separation of the coil windings.
OTOH, at comparable price points (901 vs. R100 Fuji, 90x vs. Airy 3) the Shelter cartridge will have more raw slam. The Shelter's leading edge transients will be more aggressive. Bass power goes to the Shelter, bass tunefulness and texture go to the ZYX.
OTOOH, if you can afford a UNIverse then the contest is over. Shelter does not make a cartridge that comes anywhere close, in any sonic parameter.
TriPlanar VII and SME V are both great arms. TriPlanar gives you the advantage of easy height adjustment, which many find critical with modern styli. SME gives you superb build and finish, and easier fine-tuning of VTF. Search for my thread called "TriPlanar Tips" if you want a sense of what living with that arm is like.
Good luck and happy hunting,
Doug