i've tried upsampling while listening to some CD's. and i didn't notice any difference in sound quality.

i usually use bypass anyway..
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Outlaw Audio 990 pre amp
Adire Audio sub (SVS 12.2 driver)
CAL Alpha tube DAC
Parasound P/HP-850 2 CH pre
Pioneer PL-530 TT
Polk Audio SDA 2B
NAD 2600A amp
Danger Boy here