I think you might really like s7 Scheme. Full TCO, mostly R5RS, and full Common Lisp style macros with keywords, gensyms and first class environments. And it embeds in C in a snap. I'm using it for Scheme For Max and loving it. Based on what you're saying I think it might hit the sweet spot for you.

https://ccrma.stanford.edu/software/snd/snd/s7.html