Mark IV - Slave Level Adjustments (Best Practices)

[SonVolt]

I'm using the Slave Out of my Mark IV to send a line level signal to a Matrix GT800 stereo poweramp for a W/D/W configuration. I'm a little confused on how best to balance the slave out level with the volume controls of the power amp. Is there "best practices" recommendation? Should I start with the slave level knob right up the middle (5) and adjust the power amp volume to taste, or start with the level knob at 0? My Triple Rec slave out level sits right at 5 (12 O'clock) and sounds great, but the Mesa Mark IV's slave level gets hot quick, like 2-3 on the knob. Just curious how you guys would approach this.