Thank you aniwolfe and xenolith. I have a pair of NX-Oticas and a GR Research dual subwoofer which I built and I love. I've sent an email request for advice to Danny, and waiting for a reply (very busy guy, I think).
Also, the mini-lithium batteries, what a great thing to know !, and so much better than adding an external 24VDC supply. Now the next items on my list after preamp repair.
Thanks guys!