Xonar DX and STX 0dBFS input and output voltages

Xonar DX
Input: 2.08Vrms
Output: 1.69Vrms
Input dB required for 1Vrms = -6.4dBFS

Xonar STX
Input: 2.06Vrms
Output: ?
Input dB required for 1Vrms = -6.3dBFS

For a while I've been posting my measurements in dB. That's because I have no idea what voltages they are - I measured with Xonar DX and, like with any sound card, the program gives me the numbers in dB. And I had no idea what Xonar DX's input 0dBFS was so I could convert to volts. I have a Minipa ET-870C multimeter, but it is too imprecise and inaccurate.

So today I used a Fluke 19 at my workplace to measure the output of my PSP @ 28/30. I got 179.4mVrms, while a Fluke 117 got 0.180Vrms. I'm going to follow the Fluke 19's reading.

The PSP gives -21.3dBFS into Xonar DX's input, and that is 179.4mV, so 0dBFS would be 2.08V. One small issue with measuring software is that they only show down to 0.1dB, but that is 1.16% more compared to 0dB, and that is small enough an error for me.

Then, at max volume Xonar DX's left channel's output is -1.8dBFS of the input, or 1.69V.

So from now on I'll be posting voltage measurements in volts and no longer dB.