At this level, there isn't much of a real difference. Side by side, you could likely hear something. Or, if you replace an amp you've had for a while, you could probably tell there's been a change. The best thing to do is go for a listen or arrange for a home audition. You have to decide for yourself if these differences are worth making a change.
I recently replaced my Bryston 7B ST's for a pair of Pass x600's. The Pass' seem more delicate and detailed, with notable liquidity and purity in the midrange. The Brystons seemed stronger in the bass, more substantial or in-control -- functionally slightly louder. Not that I feel the Pass is deficient in the bass, just that the Bryston had more presence in that range. The power outputs are in the same ballpark, with the Pass nominally ahead of the Bryston. I don't often play my system loudly, so my observations pertain primarily to low to moderate volume levels.
I have only listened to Mark Levinson and Krell gear in stores, with a decent 20-30 minutes to listen to each, without A/B capability. Quick impressions I had are that Levinsons sounded quite neutral and slightly laid back, while Krells sounded more colorful, dynamic, with a more distinctive bass range. A jaded critic (not I) might describe them as boring and fatiguing, respectively, although the differences were actually quite minor, and one has to exaggerate to reach these characterizations.
Whether you upgrade depends on your economics and compulsiveness with respect to ignoring vs obsessing about small differences, sometimes differences that are not really as fully audible as seems to be reported by others. Of course the rest of your system makes a difference, although you should be able to hear amp differences with your Maggies. I think the cumulative benefit of small improvements can add up to a meaningful upgrade in sound, so I tend to obsess about small differences. Woe is me. Good luck.
