If you want to avoid the Project Mix preamps then you will need to use an external preamp
with a digital outputs as the Project Mix line inputs are likely to simply be attenuated
and then sent through the preamps anyway.
Which unit you get is really a matter
of taste. My preference would be to use a neutral mic preamp and then do all the eq and
compression in your DAW. Take a look at the Audient range for something suitable.
JRP Music - Audio Mastering and Restoration.