I can answer this question. There are 3 differences between the preamp and the buffer.
1. the buffer has no HT bypass, the preamp does.
2. The buffer has a set of fixed outs, the preamp doesn't
3. The buffer has NO gain, the preamp has 16db of gain
Now for the sonic differences. Danny and I both have a-b'd between the pre and the buffer, him in his system and myself in my system. We both found that if you use the same tubes in each device that they sound exactly the same, neither of us could detect any differences. I personally like the buffer due to the wide range of use with the volume control, but on the days when I need Chinese drums at 115db levels,

I must use the preamp! So in this case I cannot say 1 is better than the other. It's more like both are wonderful which 1 do I want!

Gary