no, since this is a live sound board this is not neccessary
but the preamp deals good with line signals as well, so if you want to use a special preamp
there should be no problem to set the preamp to match the level of the external preamp
There are several possibilities to add inputs in the digital domain, especially Dante or AES/EBU. If the external preamp can convert to a digital signal, it should be possible to bypass the dLive preamps. Maybe the AppSys Multiverter is also worth a look if the preamp supports digital formats like Madi oder ADAT.