Probably the best multi-channel analog computer sound card is the Xonar Essence Stx with the 5-channel daughter card. This gives you a full 7 hi res channels. Both cards allow you the ability to swap op amps. The versions with the 5-channel daughter card are rare, but they can be found:
https://www.ebay.com/itm/ASUS-Xonar-Essence-STX-II-7-1-Internal-7-1-channels-PCI-E-90YA00NN-M0UA00/164228634040
There are not any sound cards with HDMI outputs. However, you may be able to use a video card with HDMI output to connect to your MX122 processor. I don't know how this works because I haven't done it.
Alternatively, you can get a used standard Asus Xonar Essence and use the digital COAX output (which is going to be a lot better than the toslink you currently have). This will support multi-channel and Dolby Digital / DTS.
https://www.ebay.com/itm/ASUS-Xonar-Essence-STX-II-7-1-Internal-7-1-channels-PCI-E-90YA00NN-M0UA00/164228634040
There are not any sound cards with HDMI outputs. However, you may be able to use a video card with HDMI output to connect to your MX122 processor. I don't know how this works because I haven't done it.
Alternatively, you can get a used standard Asus Xonar Essence and use the digital COAX output (which is going to be a lot better than the toslink you currently have). This will support multi-channel and Dolby Digital / DTS.