Use Kemper to record vocals?

i assume that you could. with a dynamic mic. you would hypothetically need to edit an initialized rig to make it completely clean. initialized rigs are "crunch" guitar tone by default. i'm not sure what could stop you from using a non-powered mic with the unit.

Many channel strip and studio preamps are available on RE.

Indeed that works for microphones which do not need phantom power of 48V, i.e. any condensers. This is what the Kemper can not deliver. All the rest works like a charm. I do use my SPL Track One Channelstrip to form the mic signal with slight compression, de-essing and some EQ and then route it to the input (and sometimes to the return). That is pretty clean and uncolored sound then

If you want some coloration on top you can as Kellerblues said use some profiles from RigExchange which were made with Avalon, Neve and other consoles or preamps (or their emulations). Search for author "Downfall Studio" and you'll find a handful which worked well for me.

You can still use a condenser mic, you just need a separate phantom power supply between the mic and the Kemper.