I have most of the boxes (or something very similar) suggested on this thread - just not a pair of SBLs to make the comparisons! All have been played through ES14s, which 'might' be an acceptable indicator of what you could expect...
A60 (full service) - Volume control better (and quieter!), bass tighter and highs a tad more refined. The A60 was never warm-sounding, and post service there is more articulation alongside the great midrange and sense of fun.
Naim NAT05/FC2x - same power rating as A60 but very different. Faster for a start. the A60 sounds excellent but it is only when I switch to the NAT05 that the difference in PRAT becomes clear. The NAT05 doesn't quite match the full-bodied sound of the A60, but the NAT05 keeps up with complex arrangements in a way the A60 sometimes struggles to hold on to. I know folk go on about the NAT02, but I think the NAT05 is one of Naim's best integrateds; super-flexible, articulate and fast, it has a lyrical quality missing from later Naits.
NAC62/NAP140 - has the body of the A60 and the pace of the NAIT05 but switches everything up a gear. Plenty of visceral thrills here. Upgrade with external psu makes bass rock-solid and adds richness to the mids.
SuperNait Mk1 - bags of power really grabs hold of the speakers. Introduces a whole new level of bass compared to any of the boxes listed above. More even across the frequency range (everything above is a bit mid-forward).
just my experience - and not through SBLs