Pre for Cayin's integrated?

Hi, the manual of my Cayin a70t says that it's possible to use the amp as a power amp. I was wondering if anybody has tried connecting a preamp to it and with what result.

I have the Cayin 100 and use the VAS Citation I preamp with it in bypass mode which makes it a power amp. Works great. In bypass mode the remote will not control volume, it must be done from the preamp. Cayin/VAS makes great products that produce great sound, and great value.
Do you have to jump the amp/preamp sections in the back or does the signal run through the preamp section at a fixed volume?