I recently brewed a quad (Denny's 400th Batch recipe) with 2 lbs of dark candi syrup.
There's definitely sweetness there, but it fermented out further than I expected (after a long stall in the mid 20s). I may have gotten more attenuation than typical, as I pitched some more yeast from the yeast cake of a recent batch to get it going again. Regardless, my experience is that the dark syrups are highly fermentable.
My other thought is that the Abbey yeast is going to give you a beer that is more BDS with some English character.
It's been YEARS since I brewed it, but I did a strong ale previously where I fermented with a low-attenuating ale yeast (can't remember which) and then transferred the batch onto a cake of 1762 to finish. This gave some Belgian character, but not over-powering. At the time, I was just looking to get it to ferment out to a lower FG and not looking for any specific character.
I'm not sure that it's repeatable, or that it would give you what your looking for, but it might be another option to consider.