I'm still open to any information or suggestions.
_Buying Win7 ( just so that you can implement WASAPI loopback ) may not be the best approach to accomplish what you want ( ie; run REW through MC17 & then back out to your soundcard ).
_As of this morning, I've successfully had REW streaming audio through VAC into MC17 ( by "wrapping" VAC with ASIO4ALL to make the VAC stream accessible as an ASIO "input" & then linked into MC17 via the "ASIO input function" ) . This was on XP Pro SP3 .
_I succesfully created a few new "clean" soundcard calibrations ( without glitches ) as a "proof of concept" ( for this type of circuitous routing ) .
_One of these "REW calibrations" even had EQ applied to it via MC17's DSP engine .
_You'll need to use REW within JAVA/WDM mode ( not ASIO ) for this to work .
_No sputtering , grit , drop-outs , etc. ( though I had plenty of those yesterday when trying to get two "instances" of ASIO4ALL to play nice together / just so that I could try to have REW work within an ASIO mode / never did happen cleanly ) .
_I'll post some pics ( of all the successful ) settings, somewhat later .
_If your RME soundcard ( used for input & output ) doesn't come with WDM drivers / then this approach won't work .
_If you are going to attempt to use separate sound-cards for input & output, then you should be prepared to synch them together via their respective "word clocks" ( assuming they both have that functionality of I/O ) .
_VAC ( Virtual Audio Cable ) is available for purchase
here ! _ASIO4ALL_2_11_Beta1_English_download