How do I get my HDMI audio working?

I'm pretty new to Linux but have some terminal experience from networking/IT classes. I've tried searching (a lot) but can't figure out what I need to do .

I'm on Ubuntu 17.10 and using the system as a HTPC. My video card is an older ATI Radeon HD4650(RV730). I'm using the open-source "RadeonDrvier". The HDMI output of the card is connected to a 7.1 AVR and then a 4K HDTV.

My problem is that I can't get anything other than stereo to be output. When I go into setting>sound I see the card, but the only profile listed in "Digital Stereo (HDMI) Output).

I think that the problem is that my EDL (from /proc/asound/card0/eld#0.0) shows sad0_channels and sad1_channels shows "2".

Also, alsamixer only shows S/Pdif.

I know a the common response will be "buy a new card" but I am disabled and beyond broke. I have two of these cards and they work fine on Windows, I'm just hoping I can find a fix until I can afford a new 4K GPU.

Thanks in advance!

PS - get-edid produced the following output.

Section "Monitor"
    Identifier "SONY AVAMP"
    ModelName "SONY AVAMP"
    VendorName "SNY"
    # Monitor Manufactured week 10 of 2009
    # EDID version 1.3
    # Digital Display
    DisplaySize 1110 620
    Gamma 2.20
    Option "DPMS" "false"
    Horizsync 15-135
    VertRefresh 24-75
    # Maximum pixel clock is 600MHz



#Extension block found. Parsing...
    Modeline    "Mode 10" 74.25 1920 2448 2492 2640 540 542 547 562 +hsync +vsync interlace
    Modeline    "Mode 0" 148.50 1920 2008 2052 2200 1080 1084 1089 1125 +hsync +vsync 
    Modeline    "Mode 1" 148.500 1920 2008 2052 2200 1080 1084 1089 1125 +hsync +vsync
    Modeline    "Mode 2" 148.500 1920 2448 2492 2640 1080 1084 1089 1125 +hsync +vsync
    Modeline    "Mode 3" 74.250 1280 1390 1420 1650 720 725 730 750 +hsync +vsync
    Modeline    "Mode 4" 74.250 1280 1720 1760 1980 720 725 730 750 +hsync +vsync
    Modeline    "Mode 5" 74.250 1920 2008 2052 2200 1080 1082 1087 1125 +hsync +vsync interlace
    Modeline    "Mode 6" 74.250 1920 2448 2492 2640 1080 1082 1089 1125 +hsync +vsync interlace
    Modeline    "Mode 7" 74.250 1920 2558 2602 2750 1080 1084 1089 1125 +hsync +vsync
    Modeline    "Mode 8" 27.027 720 736 798 858 480 489 495 525 -hsync -vsync
    Modeline    "Mode 9" 27.000 720 732 796 864 576 581 586 625 -hsync -vsync
    Option "PreferredMode" "Mode 10"
EndSection