A number of things could cause this (I assume you are connecting via HDMI):
1)Your amp doesn't support 88.2 - you can check in the manual
2)Your amp isn't broadcasting 88.2 support in its EDID - you can check this with Moninfo
3)Your HDMI Audio drivers don't support 88.2 - I could get playback of 88.2 with some Intel driver versions, but not with my NVIDIA HDMI Audio drivers. The problem is that driver updates are pushed by the gaming community who have a very loud voice with the video card manufacturers and they wouldn't even notice that an update broke 88.2 support, so the manufacturers may not even know.
4)Something to do with jriver's WASAPI implementation - VERY unlikely!
You may also try WASAPI and WASAPI - Event style. I recall one, but not the other working for me with 88.2 (and 176.4) when I did have it working.
If you have a spare optical/coax SPDIF cable then you could try and get it working through that, just to see if it is possible because the optical/coax port will usually be run by different drivers - probably Realtek in current MoBo's
You can sort of check if the drivers support 88.2 by looking in the Windows Audio dialog at the supported formats. If 88.2 isn't in there then MC won't work either. If Windows says yes, but MC says No, then there may be an issue I guess, but again probably driver related.
SBR