By BP-60, do you mean the B60 integrated? BP series are preamps, and there's no BP-60 preamp.
If the B60 can be upgraded or not depends on what's currently in it. Mine was at the point where it just started to be able to be upgraded, as it was one of the first with a different board of some sort in it. Mine is serial number 601400, and date code 9932 (can't believe I can remember those off the top of my head). If your B60 is after these, I'd say you have a good chance of being able to upgrade it. If lower serial number/earlier date, you may not be able to.
Call Mike Pickett at Bryston Canada. He's the guru that James will tell you to e-mail/call. I'd say call, because there's more dialog and questions and answers that way.
Not sure what's available for your B60 or what'll be involved. My upgrade cost $120. Very reasonable IMO. A friend on another forum had an older amp and preamp upgraded. His cost was very reasonable too IMO.