I think you might have answered your own question, to a degree. I don't think there are many devices on the market that have RCA/Optical out with microphone input. Creative probably the few things I can think of. Soundblaster X5 springs to mind.
So then I assume you'd need a gaming DAC/AMP; GSX 1000, Schiit Hel 2 or SoundblasterX G6 and pair that with another DAC/AMP for speakers?
I think between £150-200 the iFi Zen Dac V2, Fiio K5/K7 or Topping DX3+ Pro are generally the recommendations. At £300+ you start to get into seperate stacks; Topping L30/E30, Schiit stack etc.
EDIT: Or another option would be to run the 'gaming' DAC/AMP with Optical out to the speakers which would then use the speaker's own build in DAC.