I don't have Stirling LS3/5a, but do have Chartwell 15 Ohm LS3/5a, home made Clone LS3/5a and two pairs of JR149, In my view, the LS3/6 / Export Monitor is quite a bit better, much bigger of course.
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It's a shame that most people want the Rogers/Spendor/Chartwell etc version of the LS 3/5a's as they are all pretty old now and may well need some work but my Sterling version is the very last production for LS 3/5a's but nobody wants them.... I seem to remember Ken Kessler rating the Sterlings very highly though...
I'm sure that the Sterlings are very good, I bought my Chartwells for £90 decades ago from a friend when that was the going rate. He bought them new, they have not been abused. Crossovers in LS3/5a are unlikely to have drifted unless abused, no electrolytic capacitors in them. My clones and the Chartwells sound very similar.
No equalisation was used, output from an old Soundblaster 5.1 PC card directly to the £10 or so TPA3116 amp. There may have been a very very slight lift of the high end treble caused by the output filter caps of the 3116 being more suitable for 8 Ohm nominal speakers. The LS3/5a are supposed to be 15 Ohm nominal.
Complete vintage Yamaha pro system - love the amp