Hi,
The options you refer are two seperate things. The RT DNA/RT DV25/DV25 options refer to whether or not you are using the DNA box to output a signal, a firewire cable through the DNA box or just a direct firewire connection. The numbers available are 8 or 10. This is the RGB bit depth the theory of this is best taught through further reading (look for a book called the art and science of digital compositing), but essentially 10 bit gives a huge amount of additional variations of colour fro mwhat 8 bit offers, in fact the figure which i cannot recall off hand are surprisingly high for a 2bit per channel increase. Getting back to the issue of 8 or 10 for your digital cut, i could be wrong as im not much of a DV fan but unless your using a format like SX,Digibeta and DVC pro 50 your not going to get any benefit from 10 bit, and also you would need to be creating MXF media instead of OMF in the AVID to take advantage of the 1:1 10b option.
Hope that helps