Another preamp for my setup?

Hey everybody!

So, at the moment I am using the MR816 + ISA one + Blue Robbie = as my recording setup for a total of 10 channels simultaneously. However, if I wanted to add another preamp to this setup for whatever reason, is it possible? For example is it possible to override one of the preamps on the MR816 and replace it with a outside pre and only use the AD/DA converter of the MR816 and would it degrade the sound quality of the outside pre to use it this way? That way I’d be using 7 channels of the MR, the ISA, the Robbie + another outside pre for total of 10 channels.