I recently purchased the ETF5 analysis software for use in calibrating my system. I've just started exploring its capabilities, but have some fundamental questions about how to best use it in my HT system. The tricky part is that I have a HTPC as a source and I have been trying to use its sound card for the ETF analysis. The sound card is a M-Audio Delta 410 with 8 analog outs, 2 analog ins, and S/PDIF in/out. See my sig for the full system configuration. I'd like to be able to measure the frequency response of each speaker in turn as well as one speaker and the sub at the same time. My problem is, how do I get the software-generated test-tone to output to both the speaker and sub at the same time? When the sound is output to the analog outs from the card, it goes only to a single speaker. Is there any way to have the software-generated test tone output through the digital output of the card to my receiver? That way, the receiver will handle the bass x-over and sound will be output to both the speaker and sub. The hookup I've been using for the tests is: L channel OUT to L channel IN R channel IN to microphone R channel OUT to receiver I've read through all of online tutorials, but it seems like I am missing something fundamental. Any suggestions? BruceD? As a side note, I started out using the Rat Shack SPL meter as a mic (w/o correction), but quickly realized that I would be better off with the calibrated mic and preamp sold by ETF. The SPL graphs of my front speakers rolled off sharply at 12,000 khz, which I believe is due to the microphone, not the speakers!