Your link is weird, but I assume you mean the "(Current)" one.
An LFO module of some kind (Ochd, Batumi, or whatever seems fun to you)? Maybe even a spring reverb for that classic Easel sound. It's hard to go wrong here. Maybe even a filter if you want to expand your palette beyond traditional Buchla sounds while keeping things fairly simple and focused.
I would rank my suggestions here in the order they appear in terms of relevance/usefulness.
I suggest keeping the ring modulator, too. They sound great with the 258t sine waves and it can also act as a bipolar VCA.
-- Zacksname
Good advice. right next to my current (yes that the one) setup, I have an Behringer 2600 GM. This give me four LFO, sample and hold, a filter, spring.. all the 2600 bits.
I guess I want something unique but still west coast.