LDR Active Preamp - does it exist?

It's not LDR, but I think a preamp like the W4S STP-SE is what you're looking for. If it isn't everything you hoped for, well, they take returns.

Your best bet is to deal with your gain issue at the amp. Choose one with higher input sensitivity and a passive line stage will match just fine, no extra gain needed.

Shakey

I already owned the amp which input sensitivity at 4V. These amps practically eliminate the use of passive pre, even using Tekton Lore speaker rated at 98 dB, still does not provide enough loudness and dynamic. It would be a surprise to me that no other commercially available active preamp (tube preferred) that utilized LDR volume control.