I'm not familiar with the B2B-2 preamp/DAC, but I have a PBN Olympia LX preamp that I paired with the Liberty Audio B2B-100 amps when I owned them. I purchased it from a fellow AC member. Liberty Audio and PBN Audio are the same owner/designer (Peter Noerbaek). All I can say is that the LX preamp is incredible and I have no desire to part with it!! Overbuilt, high-quality parts, proven design, and excellent customer service. It appears that Liberty Audio follows the same philosophy.
The downside to the B2B-2 preamp/DAC is what it is -- a combo of a preamp and DAC. It may not be cost-effective long-term if you want to swap out DACs in the future.