I restored my dad's original 2000 II with the BD 4136 adapter and OPA2134's fitted along with new muse caps and it sounds fantastic!! I left the 4739 alone since there was nothing viable at the time. FF to now, I have a 4000 II I bought with one dead channel that I'm tracing down to possibly a dead 4739. I've read that someone here has used it though I don't know which amp(s) were tried, but there are mostly the same amp options as the 4136 adapter. What are the considerations when selecting an amp for the 4739, and has anyone had any luck with replacing with one of them with one from BD?