I have been working towards getting my QA401/471 to be my primary equipment for measuring and designing speakers. Currently am using a minidsp HD to design a 2-way active speaker. I appear to have gotten the ASIO drivers for the QA401 working, but once they are, Windows 10 stops recognizing the minidsp and cannot connect it all. To get it back, I have to yank the QA401 USB connection and reboot.
ASIO is generally an interface for a single application. And once one application has opened it, another application cannot. Are you using ASIO drivers for the minidsp or something else?
I abandoned my use of the QA401 for speaker measurements mainly because I need it for amplifier measurements in another room. Am still using the QA471 with a soundcard and I can switch between REW and the minidsp app just fine. One difference is I installed the ASIO4ALL drivers and that may have allowed better management of the apps for each device.
So, just in case it helps others or someone knows of better solution, I tried my QA401 again as it is better built than my DIY breakout box. I got it all to work pretty well in Windows 10 with ASIO401 and ASIO4ALL installed.
I was able to do dual channel measurements with the released version of REW but the lack of level controls made this difficult. Notably when dealing with a more sensitive driver like a tweeter. Once I configured the setup to measure the woofer, had no way to keep the same setup and measure the tweeter without changing the sweep level (or risking hearing damage). Am not sure I could have calibrated the QA401 without the QA471 providing additional input gain.