That is quite a system for an admitted novice. Aurender suggests that SPDIF is the best choice as an output over USB due to their high quality clocking, and given the choice between bnc and aes, aes will always win. On the other hand it looks like MSB is good at handling USB.
i would definitely upgrade to AES, but I would also try USB. You owe it to yourself to find out which sounds best in your system.
My system is not at that level, so I can only recommend cables I have tried that sound better than the rest. I am sure there are better ones, but it might be best to start with lower cost options and then go up the chain once you decide on a path. Acoustic Zen MC2 AES is a decent cable, and WireWorld Platinum USB is another good choice. I have used both of these and compared them to others and they rose above.
Keep us posted on what you find.

