"The engineer tells me that when HDLink is reading the file, it is decoding it at 4:2:0 (8-bit), that's why it thinks it needs to up-sample it to 10-bit. So HDLink is doing more work than it needs to. For the best quality 10-bit quality conversion of these files, you should batch convert them in After Effects."
Make of this what you will. I have to confess, I'm a bit confused. If it is "decoding it at 4:2:0" is it chucking away info? I will try the AE route in CS5. Never used this method before.