Bryston 4B3 or 14B3 ?

I just bought a Bryston headphone amp and owned about 5 other 2 channel Bryston amps. I would not pair Bryston with any speaker with Beryllium. Not sure if this Focal has Be.

If you are using a Mytek for your DAC, strongly suggest you use a preamp.  I've had several instances of static causing the volume control to hit max.

BHK labs measured the 4B3 at 354W into 8 Ohms, and 552W into 4 Ohms.  Bryston is conservative with their power ratings.  I chose the 4B3 to power my Magnepans and find it to be perfectly neutral and clean. I can not imagine ever needing more power or SPL than is provided by my 4B3.  IMHO it is the sweet spot in their line up but I do use Tube Pre-amplification to add texture. There is a difference in input impedance which made the 4B3 a better choice for me. The 4B3 measures at 29k/20K balance/unbalanced.

What is your current amp?  Have you heard your focal speakers paired with a Bryston amp?  Focal are very fast responding speaker, but can sound sterile sometimes.  Bryston is also fast and very clean, but not textured.  This pairing may cause the sound to be too bright/thin/sterile.

If money is not an issue, then my recommendation is to go with the higher wattage amp.  Focals typically have some fairly significant impedance dips and sensitivity is often overstated by manufacturers (although I haven't seen the measurements for the 1038be).  Having more wattage is never a bad thing, especially if you sometimes crank the volume up and listen to music with a wide dynamic range.  In addition, if you ever change speakers in the future, the 14B3 will drive them no questions asked.  

That being said, Bryston makes very high quality amps with a consistent sound signature. 300wpc is an honest rating from them, and you're not likely to run out of power.  If you aren't trying to fill a huge room with high volume (and you want to save some money), then the 4B3 would not be a drop off in sound quality.

Just my two cents,
Scott