What are you using to send audio to your monitors? Are you using the same interface on both computers? What drivers does the interface use? Are they the same on both computers (asio, wdm, etc.)? What about bit- depth? Btw, this is pretty much assumed, but I'll ask anyway: you aren't comparing the sound through the octacapture with an on-board sound card are you?
I swap computers all the time in my setup and I've not had this issue.