I thought seriously about the NuTube, but after doing a lot of reading on both in the DIY Audio forums, decided to go with the ACP+.
I've been running my ACAs in the parallel mono mode, but switched them to the bridged mono mode yesterday and I'm really impressed. I feel like the bass presence drops a little, but the mids and highs seem better. Maybe it is because the bridged mono is single-ended. Whatever it is, I like it a lot.
I look forward to hearing more about your preamp project when you get it finished.