I picked up a used LD I+ today, locally. Still has the stock tubes and stock op-amp chip. However, I plugged my Squeezebox (Burr-Brown DAC) into the amp and used my HifiMAN HE-400s with it. The sound was excellent! I don't have much of a hybrid amp background to compare it to, but I did have the HifiMAN EF-2A for a few months. However, I fed it a signal from an iPod, which I realize now wasn't good at all. I would have loved to hear the EF-2A with the Squeezebox. However, I now need to lift the cover and check the position of the gain. I'm running it at about 10 O'clock and the volume seems at a good level for me.
More to follow as I read through this thread a bit more and look into some op-amp options.