Hi,
The point of the Transporter is that is has its own DAC's
If you are going Transporter to BDA1 then it might be better to get a Duet.......
Or go balanced Analogue out of the transporter to your pre.
I would think it worth doin A/B tests yourself on those options.
Cant help with the BNC Q's.
I have all three (3): a Squeezebox 3, a Duet and a Transporter

The Transporter may find its way into my living room system...but for now I'll keep it in my main system. At this point the Transporter sounds like it has a hair improvement up on the Duet, so it'll stay for a while. The Duet doesn't support 24/48 or 24/96 files...etc.
Besides, the SP 1.7 doesn't have XLR analogue in.....the new preamp I'm getting will have it, maybe I'll try the Transporter DAC then with XLR outs.
Also, I may get a unit like the Pace Car 2 to run the word clock on the Transporter.....lots to toy with.
Keith