"So from the ART, use a "TRS into the focusrite with the switch set to line (not instrument?)" and, of course, phantom power off?"
That's how I would do it.
As has been cautioned, be very aware of the status of your phantom power.
 
T

CONSIDER the ART as your 'color' fx.....
 
don't use it on every track.
the art uses 'tube distortion' as it's 'color', more or less,
and this will create a 'sonic fingerprint' that will create a haze over multiple tracks,
because of buildup of specific frequencies and some masking.
 
just sayin'

DeeringAmps
As has been cautioned, be very aware of the status of your phantom power.

 
Not quite.  The manual clearly states that phantom power will only be applied to the XLR pins, it will never be applied to the TRS connections in the centre of the combo inputs.  They would not be that silly.  Capacitors would be used to block any DC from being sent to the TRS inputs.  Even so keep phantom power off anyway.
 
A mono jack to jack lead could also be used from the ART to the Scarlett inputs.  Some signal level loss would occur that is all.  Switching to LINE is more important.  It changes the input impedance and input sensitivity.
 
 
 

Absolutely fantastic help and explanations, thanks big time all, I'm crankin' up this afternoon for my first real session with the new pc and interface!