Barty1884 :
It depends exactly what you're looking for OP.
Both the DG & DGX can provide 5.1 over SPDIF....... but lack the software capabilities of conversion to Dolby or DTS - so for 5.1, the raw audio needs to be in one of those two formats (DVD, Bluray etc).
If you're dealing with differing formats (PCM, for example), then you'll be limited to 2.1 as it will not 'convert' to Dolby or DTS.
If you want true 5.1, with the ability to convert other sources to a 5.1 Dolby or DTS, you'll have to clarify your definition of 'cheap', as those are (generally) $100+
It's a bit more complicated. As it is, I can't get surround via optical cable even if I watch a movie that supports 5.1 channel. Did some research on that and found a modified driver (some goood guy, forgot his name) that "unlocked" my Dolby Digital Live and DTS on my Mobo sound card (cool, right?). After I managed to finally unlock those options (it is quite difficult) I was able watch movies and hear all my 5 speakers work. Even when I was playing music I, all my speakers did work, more or less. Center, right front and left front were working pretty smooth and right back and left back just some background sound, but hey, they worked. Therefore the overall power output of my system was obviusly bigger than just 2 speakers working.
The only problem was, since it is a modified driver, when I was listening to headphones, I was hearing all sorts of pops and clicks pretty often, which is a very unpleasent thing.
I recently upgraded to Windows 10 and yet again I can use only 2 speakers when I want to watch a movie or listen to music. I don't really want to repeat that pops and clicks experience again and I thought to invest some money in a sound card to solve my problems.
Since using SPDIF is my only option (my home cinema reciever doesn't have HDMI IN) this is my only option to listen to surround sound.
If I'll buy this new sound card, I will be able to listen to 5.1 channel during 5.1/7.1 supported formats like Bluray and DVD as you mentioned, but music only in 2.1, leaving the 3 speakers with no sound in them, right?