Thanks very much guys. That's really helpful. I think perhaps I'll look into the powered monitor option. The Adam one looks good, and I'll have a think about whether that will work or something similar.Thanks again!
What did you end up going with? I'm also new to theremins like yourself and ended up taking Thierry's advice on this forum where he mentions, "I can recommend (since I own one for a long time) the Behringer K450-FX. It's a 40W amp with a 10" speaker and some digital effects (Reverb etc.) built in. It is not expensive (about €150 here) and the most important: It's THE amplifier on which I did the whole bass module developing and testing (the ESPE01 module).
I bought a new Etherwave Standard I found in the wild, and the Lost Volts LV-4. Both should be arriving next week. Like you I was reading for hours and hours on various sites, including this one. And from what I gathered, a keyboard amp was best suited for the line level output of the theremin, as well as the frequency range. So I went with Thierry's suggestion of the Behringer K450-FX. I'm picking it up today from a local eBay seller for $100, quite a deal!
I look forward to posting my progress once everything is put together here at my studio. I'm curious to hear what progress you've made thus far!