Tube DAC for Croft 25/7 and Harbeth 30.1??

I recently bought a pair of 30.1 together with the Croft 25/7 combo equipped with NOS Tesla e83cc valves. I play only digital and using a Rega DAC. I'm very pleased with the sound coming out of these boxes. Feels more alive, with more separation, 3D than I ever had the chance to hear before.

However I'm getting very tempted to get more of that feeling by upgrading the Rega-DAC to a good valve DAC. I rather spend it on a used so I can get the most for my money. My budget is about £1000. What do you recommend?