Is Mark Levinson still considered up there with the best of the best?

Don't get me wrong, he was involved in some great products, and no-one has mentioned Madrigal yet.

However he was involved with so many products he was like the Pierre Cardin of HIFI.

From my personal experience  any new amp will be challenged  to keep up with a well serviced pair of 33h mono blocks. 

I have the opportunity to listen to used ML 333 and ML536 in comparison to used Krell FPB, Pass Lab X350, X600, and new generation amp

Class D amps .

For the price point , used ML 333 and 536 are still very good options and sounds better than any Class D amps 

What matters is the designer, not the manufacturer or the promoter/salesman/marketer. The designer is responsible for the sound ... the marketer just sells it. If a manufacturer changes their house sound, that means the design staff has changed or moved on to greener pastures. This turnover is pretty common in the hifi biz because the actual hands-on designers are often poorly paid and their identity is hidden behind a corporate screen of Non-Disclosure-Agreements (NDA’s). By the way, never agree to an NDA in the hifi biz, especially if it is informal or based on a handshake agreement. That’s lawsuit territory. Don’t go there.

It’s fairly easy at a hifi show to know if you’re speaking to an actual engineer or designer versus a marketer. A marketer/salesman will hide behind a screen of vague buzzwords, and will get angry and dismissive if pressed hard enough. When I was wearing my Tech Editor hat, I was thrown out of exhibit rooms more than once by marketers at trade shows. By contrast, a real engineer or designer will be quite open and friendly, and will let you know if your questions are getting too close to NDA trade-secret territory.

I’ve done both marketing and designing, and they are very different things. Marketers are often technology-averse, and fall back on impressive-sounding buzzwords that don’t have any specific meaning. If they invoke Quantum anything, yes, you are dealing with a marketer and should leave quickly if you value your sanity and your wallet.

@lynn_olson  The designers don't always get to build the amp exactly the way they want to, when working for a manufacturer. I've heard Nelson pass say that when designing an amplifier for other companies they changed this and that to meet budget.