Luxman 507/509

I wonder if anyone out there can answer a question I cant find an answer to anywhere on the internet please? I have the option of a good deal on a Luxman 509x but clearly still a fair bit more than a new 507uxII. I honestly cant convince myself of a difference in sound driving dynaudio heritage specials but I wondered what technical differences actually exist between the two - aside from a modest difference in rated power output. Any thoughts? Many thanks
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I chose the 509X and am not disappointed. Have not found official publication of the class-A bias but based on comparison of the idle power consumption to the 590 & 550 integrateds, I think the 509X is about 17 WPC class A and the 507 about 9 WPC class A. 
I asked Luxman USA in an email about the Class A envelope for the new L-509X(which I bought) and the L-550axii I was considering

Here is their response that I got:
" The Luxman L-509x is an excellent amplifier. It is considered “top of the line” and most recently introduced Luxman integrated amplifier model. It features circuit and construction details/refinements not present in (earlier introduced) the L-550aXII and L-590aXII.

L-509x is biased such that the class-A operational envelop approaches 6 watts/channel into an 8 ohms resistive load. At lower (or higher impedances) class-A operation transitions to class AB at lower output. (i.e. near 3 watts/4 ohms resistive load)".

Very interesting lower than expected class A bias. Thanks for sharing!  I wonder what all that idle power is doing if not class A bias....

Looking at the pics with lids off, the L-509X has twice as many power supply caps as the 507. This might enhance bass slam, and the 509 is not lacking bass slam in my experience!