Assuming you will use the Oppo HA-1 for the DAC or Amp, I think the the Oppo as a DAC is a relatively thin, so pairing with the GSX might not e great. Pairing it with the warmer moon might be better.
Then again, the amp section on the Oppo is relatively good, so getting the yggy now and getting a better, possible tube, amp later might be a better choice. I think you will get more a sonic upgrade replacing the Opps DAC with a Gumby or Yggy. Note, there are some that prefer the Gumby to the Yggy, so you should try to listen before you buy, if possible. Heck, if I were you, I would take a trip to Bain Bridge island in seattle and go to the Bottlehead store.