Do a search for the B2RE and you will see how much TB does not like the head. About 80% hate the darn thing and 20% say it works just fine. The built in tone of that head has bunches of low end below 80hz while scooping a decent amount at 600hz - with the controls flat! The head runs out of power fast because of the extra low end push - so it will clip early if you do not reduce some of the low end right away. Also, the sound of the head is very cold sounding overall. An edgy solid state tone for sure - usable though, but no warmth.
I owned the model before it (B2R) and I am glad I no longer have it.
If you are strapped for money,
Carvin.com - Guitars, Amplifiers & Pro Audio: Bass Heads
I own the BX1200 and love it! Warm and sweet tone with solid state clarity. Nothing too special, but the head sounds great in every frequency and it is easy to adjust the tone. Any version of a clean bass tone you can think of is simple to get on those BX series heads. It's a little strong in the treble regions, but you can easily dial it out.