I'd say the better your headphones, the more likely it is you'll feel the need for more power than the B2 line out can give.
I'd also suggest you go for a combined headphone amp/DAC: the consensus here on the forum is that an external DAC gives better sound quality.
You wouldn't get one for $100, more likely 150, but look at what you get in terms of connectivity. And check out the reviews. You could connect it optically from your B2 and also plug in a laptop to improve the sound of any music files you might have there. It's easy to switch between sources.
I couldn't be happier with the K5 Pro. I use it with AKG K702s and a pair of Grado SR325e phones. It has plenty of spare volume, even on the middle gain position on the switch and the width and depth of the sound is impressive.