This should work just fine. Make sure that you go through Settings->TV->Tuner setup. It should detect 2 USB tuners. If it does not detect both of them in the list make sure they are showing up in your device manager. I will take a screen shot of my settings/tv/tuner setup.
Your setup seems fine.
/USB --\ out
HTPC CoaxSplitter (1 in 2 out) IN--> Antenna
\USB -- /out
you do have to run the setup if you added a second one, and then after that you can record a show & watch a show or record 2 at the same time.