SPDIF trouble with multiple usb devices

[Scott Doty <scott@ponzo.net>]

So I'm having the worst luck with optical SPDIF devices.

  
http://www.alsa-project.org/db/?f=d0d48e597f0cdbd1b377aea6f8d73b000301ae8a

Recently I hooked up my synthesizer in the configuration that used to
work fine, and it didn't work:  The Sound Blaster HD usb audio device
doesn't seem to be working on modern kernels, nor does the spandy-new
SIIG HD Digital 7.1 USB Audio Box.

I'll go down the list of devices:

_[/proc/asound]_(root@eva)_
# cat cards
 0 [Pro            ]: USB-Audio - SB X-Fi Surround 5.1 Pro
                      Creative Technology Ltd SB X-Fi Surround 5.1 Pro
at usb-0000:00:14.0-4.7.5, ful

This device works fine.  Unfortunately, it only has optical SPDIF out,
no SPDIF input.

 1 [Audio          ]: USB-Audio - USB2.0 High-Speed True HD Audio
                      CMEDIA USB2.0 High-Speed True HD Audio at
usb-0000:00:14.0-1.4, high speed

Just got this from Amazon, it is a "SIIG HD Digital 7.1 USB Audio Box". 
I was hoping the optical SPDIF input would work to replace the Sound
Blaster HD below -- but alas, it doesn't.

 2 [M8             ]: USB-Audio - MOTIF ES 8
                      Yamaha MOTIF ES 8 at usb-0000:00:14.0-1.3, full speed

This is actually a MIDI-over-USB device, my synth.  The output of the
synthesizer is optical SPDIF, which _used_ to work with the following
device:

 3 [HD             ]: USB-Audio - USB Sound Blaster HD
                      Creative Technology USB Sound Blaster HD at
usb-0000:00:14.0-4.7.6, full speed

I used to be able to use the optical SPDIF input for this device from my
synth, but that seems to have stopped working.  Further, I can't play
audio out of the Sound Blaster HD's optical SPDIF output, either.  It
works in Windows 10, which is where I had to spend my latest music
session -- yuck.

Never mind the rest of the devices.

Naturally, I'd love for this to be a quick fix, but I'm even willing to
buy more hardware, if I know the SPDIF optical input works.  (Buying the
SIIG device was my way of "punting" by getting Creative out of the mix.)

I'm also willing to ship the non-working devices to anyone who can make
them work, for the good of Linux.

I use Rosegarden on Linux, and for various reasons, the port to Windows
just doesn't cut the mustard.

Any help you can provide would be greatly appreciated. :)

 -Scott