So before I got my refund on HDTF, I decided to browse the files and it appears that the synth soldiers actually have sounds (very few of them). I decided to upload it because I actually do like the sounds. I recommend you merge them together with this mod here. This mod is meant to go together with this mod here. It doesn't sound good with the regular combine soldier, only the HDTF synth soldier and any other synth soldier mod.