This situation is similar to how Maggie lovers often claim that less than ideal tube amps are wonderful with the speakers. The OP should know that the matchup of the SIT-3 and the speakers will work. Is it the optimum, probably not.
Nevertheless, the bugaboo is that even if you got a different amp that was supposedly "better" for the speakers, there is NO guarantee you will actually enjoy it more! Actual comparison is a must in these matters. I urge you not to dispose of the First Watt amps before you make a change.
I ran First Watt J2 (pair) amps to drive the Kingsound King III speakers (ESL) and although not ideal, it was among the best sounds holistically of all amps I had used with the speakers. Just because the match is not perfect in no way means you are assured a more acceptable outcome simply because of trying to match up with a more ideal amp. It's just not that simple.