I would like surround-sound, but only have a stereo mix. Can SRT make a new surround-sound version?

Yes - SRT are experts in can creating highly effective "pseudo" surround-sound versions from stereo originals. This process is sometimes referred to as "extraction" or "unwrapping". Of course this option will never sound as good as a true 5.1 surround mix, but where time and/or budget are limited, this can create a very convincing alternative.