Hi Gharrington; I've owned the standard Vand. 5s for over a year now and love them. It took 2 1/2-3 months for them to fully break-in. I've not heard the 5As as they're scarce yet. Also, isn't list price of the 5A about $14.5K?, ie quite a bit more than the std. model 5. I know it would cost $4500. to up-grade my 5s, so the 5As must be quite a bit more refined?
My system is now complete and sounds excellent. I use Levinson 37 transport and 360S DAC and consider it a near state of art front end for digital. Pre-amp is a Sonic Frontiers Line 2SE w/NOS tubes, Hal-O dampers and it sits on a Seismic Sink.
For an amp, I started with a big 300 wpc McCormack DNA-2 Rev A by Steve McCormack at SMc Audio, but as you know the 5s have built in 400 wpc amps for the built-in sub-woofers (below 125 HZ). The upper drivers of the 5s are an easy load to drive 8 Ohm load, so I've recently gone to a McCormack DNA-0.5 "Gold" Rev., and this is a wonderful sounding amp for the 5s. I gained some valuable floor space by doing this. I use mid-priced Active Shielded Syn Res ICs and speaker cables as well as SR Master couplers all plugged into dedicated Hubbell outlets.
Anyone that can afford the 5As though probably wants to spend more money for a more "prestigous" amp, but to tell the truth, I consider the 100 wpc .5 Gold a "prestige" sounding amp and it drives the 5s beautifully. I've heard that R. Vandersteen uses tubed gear with the 5/5As though-- some say ARC, but I haven't talked to him about it. Personally, I prefer a nice sweet, liquid SS amp for it's speed, PR&T, and bass control, and the .5 Gold does this.
I suspect you'll love the 5As. Good Luck with them and please report back after you've used them awhile. Cheers. Craig