Just picked up a used BH Crack (SB not installed).
Upgrading from my Magni 1, it seems like the soundstage has opened up, especially the vertical soundstage. Everything just seems more engaging and in-your-face. The bass and midrange are definitely more impactful and powerful. Vocals are still surprisingly clear, although the treble does seem to have lost its shine a bit.
Didn't notice a huge improvement at first, but it became much more obvious when I switched back and forth (volume matching as best as I could).
Overall, it seems like a great upgrade. Would a Speedball bring the treble/midrange a bit more forward?
If you have the SB you can install it to see if you like the difference, I actually didn't like the SB installed, could be the tubes that I was using. If you have to purchase the SB I would hold of and try tubes first, as always YMMV