Elinor,
The Spacearm has integrated cables that end in RCAs directly to the phono stage, so no phono cable upgrade is possible w/o doing some serious DIY work inside the tonearm, which could be risky.
However, your post got me thinkin'...
Ozzy, I'm using a Boston Audio carbon mat on my Spacedeck, it is not as imactful as adding a Neuance shelf, but it's an improvement over the stock foam mat.
Also, I'm surprised that the Promethean base helps on your springy floor. Have you tried the Neuance without the spring base below it? When I asked Ken Lyon about what if anything should go beneath my Neuance, he said, "Nothing really, but if you want to try cones, go with DH ceramics". Sounds like you've got different results than what I've seen, but I've heard VPIs with &n w/o the Promethean, and IMHO, it was better off w/o it. Regards,
Spencer