Well after facing the same decision..I decided that an outboard Phono stage was the best for the long term.
1.If Bryston releases a new preamp I won't have wasted the money when selling it.
2.More flexible in that you can use an outboard phono stage in any system.
3.I get to keep the BP26 as it was factory designed.....For me that was important,it may not be to you.