Tweater hiss

I checked it out last night and when the volume is turned up, the hiss increases in volume. If the preamp is unplugged the hiss is still there.

That makes little sense to me.

If the his varies with the volume control, it comes from the preamp or the source.

If the hiss comes from the preamp or source, it should disappear when the preamp is unplugged from the amp. Are you sure it is completely disconnected from the system and that there are shorting plugs in amp's inputs?

The fact that you isolated your amp from the rest of the system would narrow it down to a couple of possible explanations that I would check first.
1. The noise is typical of the unit (ask Bryston)
2. Try an AC line conditioner. (garbage in - garbage out)
3. If not 1 or 2, I would be asking someone smarter than myself.

Kr4 that is exactly what I thought. I was expecting that once I disconected the preamp, the hiss would go away since it increased when I turnded the volume up. I have a Audio Matrix power conditioner coming on Friday so maybe this will help. I am also having a dedicated line put in soon as well. I will contact Bryston about it as well.

How much hiss is there? Can you hear it when you are more than a foot from the tweeter? If not, it's probably OK. Otherwise, see what Bryston says.