i tried one of these when they 1st came out. i was running an aiwa 5-disc changer (modded) into a highly modded art di/o. i bought the gw-labs dsp from audio adwisor - they had a good price on a demo unit, & a 30-day money back guarantee.
on its by-pass setting, there was absolutely no change whatsoever when inserted between the cdp & dac. when the gw labs dsp was set to its 96khz upsampling mode, the system had me running from the room with ear bleed after about 10 minutes. harsh, etched, glaring. i was happy to keep my $80 rdl labs pro-audio piece, which allowed me to use my modded optical output aiwa w/the rca input modded art di/o. thanks to audio advisor for their money-back policy! aa if it were me, i'd be more interested in looking for a better dac.
ymmv,
doug s.