Thanks again Ellisdj for your thoughts and suggestions. Interesting you are picking up on two aspects that I also think are pretty important to get the GX 300's really performing at their best - firstly, the soundstage, so you hear the instruments arranged both left to right and back to front too, and secondly, using an amplification sound signature that leans towards 'smooth' rather than too clinical and bright.
From your description of your experience with Moon and your Meridian amplification that's the impression I'm getting - is that right?
I popped back to the dealer here in Singapore who sold me my GX300's (and Apex's too) to discuss what I was missing with my old Cambridge amp after auditioning at his studio. So he then compared a Primare I30 (Ithink) with a dinky little valve/transistor amp called a Music infiniti M101A. The former was S$3000 and the latter S$380! These were played through a pair of RX6's - the little Infiniti was better (to myself, someone else who was auditioning the RX6's and the dealer who had a big smile on his face). Bass was tighter, soundstage was as above whereas the Primare was only left to right. Also, the sound signature had a slightly smoother sound than the Primare.
So the dealer has offered I can take the little infiniti home for a test when i have a decent run of time home in Singapore to have a proper listen. So in a couple of weeks time......will let you know what I discover, but have serious doubts over absolute volume (with only 25 watts), but he assures me there's plenty enough to upset the neighbours. We'll see...