I have to admit I quite like having the different presentations offered by both the S/Pdif and AES connections, I find for up tempo music the S/Pdif really works but for vocal and laid back tracks I prefer the AES, also if I have a bright recording, switching over to the AES can really smooth out the top end and make it far more listenable.
I am opposite, i find the SPDIF to ease the bright recordings. This could be more cable related then actual BNC bdp1 characteristics. I have yet to hear a 192khz recording that is bright on bnc or xlr.
I find the digital connect to be dependant on the power cables employed too. Some power cables just enhance the high freq energy and i just end up using a digital cable to compensate to my own taste.
My power cables atm are a Wywire juice 2 on the bdp1

and a Harmonix x-dc2 on the BDA, thats another big

. These cables are permanent and i use the digital connects to tweak.