I wouldn't discount the fact that the new BF boards might benefit from a little "break-in". I'd be more interested in impressions/opinions after a week or so of use and see if things change or "settle in".When directly comparing the two:
B1 - Slower. Less detailed and resolving. More linear of the two but still has a lower mid/bass bump. More euphonic. Warmer. Easier to listen to in the background. Sounds great. Easier on the ears using headphones. May be too relaxed for some. I prefer B1 for headphone use.
B2 - Faster. More detailed and resolving. Wider FR&Staging. Upper mid/lower treble bump. More fleshed out and engaging bass that can still slam when called upon. Sounds great. Might be too sharp for some. I prefer B2 for speaker use.
Pick your poison. These boards have some pronounced sound differences that could make or break the synergy in your system. I'd wager that the future secondhand market for Bifrost 2 owners with both boards will demand a high price. Another poster had mentioned $100, I'd value the OG board at $250 - the original card is no slouch and has it's own strengths.