What SQ value does a high end stereo preamp add to a network player?

The Lumin has a good attenuator, there is no discerible benefit from adding a pre since the output voltage of the Lumin is more than enough

If the Lumin X1 is your only source,  Lumin’s Leedh Processing 
should be fine . No need for a pre amp.

Thanks, very helpful but its part of a ht system so i need a means to switch between whats using speakers.

Only use network player and av processor, ie no cd or turntable.

can i use x1 as a pass thru from ht processor for mains?