Something weird happened after upgrading to 64bit.
I have a DAC connected to the USB and an AVR to the HDMI. The AVR is Windows 10 default sound play device. I started the evening listening to music through the DAC and decided to switch to a movie. what I did was:
1. Exit Theater view
2. Change the JRiver audio device from USB DAC (WASAPI) to AVR (WASAPI)
3. Go back to theater view and select the movie
4. No sound.
5. Exit Theater view, check again the audio interface. It's set correctly to the AVR (WASAPI)
6. Exit JRiver, reboot PC
Second and third try with reboots after each fail and still no sound from JRiver when watching a movie. But what I saw from the USB DAC display panel is that it was receiving an audio stream from the PC, despite the setting in JRiver that selected the HDMI audio device and despite the DAC not being the default system audio device. I decided then to try another trick: I switched JRiver to the default audio device, which use direct sound and got the soundtrack back.
So right now it looks to me like 64bit has some problems switching between WASAPI audio devices and may in some case remain stuck with the last one until forced to use the default direct sound device.
The other issue I noticed is lack of soundtrack and video synch. I know that video process can cause a delay of 100-300 msec, but in my case what I experienced was an audio delay of a full 1 second which is excessive and unexplained.