I... Eh, I don't really like either of those, not for this roleplay. The classical tone doesn't fit a Martian roleplay based in the red desert and such, and I don't really like Two Steps From Hell in general.

Really, I listen to specific soundtracks for specific scenes. For instance, when writing for La Parranda I find myself wanting to listen to some guitar with a Western / Space age feel to it. For instance, [url=https://www.youtube.com/watch?v=6VVGVx2gTJ0]this[/url] piece from Borderlands 2 is perfect for my writing moods in La Parranda.

I've got other tracks lined up for battle scenes, such as basically the majority of Borderlands 2's soundtracks, but since I haven't been in a battle yet I haven't needed those. There's a few other games and artists out there that have the right sounds I look for in combat music and still fit the space theme. [url=https://www.youtube.com/watch?v=oLA0vB9LCTM]Bastion[/url] has a lot of good Space Western songs that work for battle. There are also tunes from [url=https://www.youtube.com/watch?v=IXAw7BBV-Zk]Starcrawlers[/url] that work well for combat and non-combat purposes. Doc Sam's. Also, [url=https://www.youtube.com/watch?v=8z_a33jFUds]FTL[/url] and its expansion have some decent tracks.

For a theme that belongs to the whole roleplay, though...? I haven't really given that much thought. I'll have to chew on that one.

EDIT: Yes, I listen to lots of video game OSTs.

EDIT 2: And the theme would have to be gritty enough to feel like Mars while also having something that spits of Skyguard and the Corporations.