I love my Bifrost. Mine is still all stock, but it's connected to a Simaudio Moon Stellar and sounds excellent.
As far as the stock Bifrost sounding a bit edgy or lacking a little in the bass, I can't see how. This thing is silky smooth with plenty of detail, oomph and air. IDK, maybe the stock unit has those traits but the Stellar tames them. Funny thing is, I use NHT 2.9's which people claim are also bright. Again, I don't find them to be. Then again, being powered by 25 watts of Class A power might have something to do with that as well. I say it's all about system synergy.
I do plan on getting the Uber upgrade board at some point, but not just yet. I have another project that I'm trying to work on and need to save my funding for that.