Question i currently have a geforce gtx 960 fitted to the pc ,and a radeon r9 270 that is not fitted

Other than the fact I don't know anything about Stream Labs and if it will benefit from the second GPU, these are things to consider:

  • Is your power supply good enough to run both cards?
  • Will it physically fit in your case?
  • Do you have adequate air flow so your primary GPU does not overheat from the extra heat coming from the second GPU?
  • Have you considered a capture card instead?