That doesn't make much sense. So, Dan spends all that time and money developing the Momentum and then scraps the topology to spend more time and money on another design, only to then go back to his original design for the lowest product in the range.

That's not generally how a business works. First, you build a halo product - in this case, the Momentum. Then you decrease costs for casing, use cheaper components and decrease complexity as you go down the chain so there's a consistent family "sound" and you are not reinventing the wheel along the way. This ensures that (1) your R&D spend efficiency is maximized (2) you can release products of lower lines within reasonable time frames to capitalize on the halo product hype and (3) maximizes the chances of a customer staying with the company as they move up the chain since it's more of what the customer already likes as he moves up the chain.

I heard it with Kef Ref 5s and SF Serafinos the other day. Compared it with MC275 amp in stereo doing A/B ing back and forth. The salesperson and I kind of liked the Mac on either speaker. Just a tube preference really I think.
Full disclosure, I was there looking for speakers, so not as focused on the amp, but we both liked the two speakers with the Macs.
Warmer, better mids and similar highs. Bass was all you could want on both amps.
Room was not ideal as dealer is really a high end custom installer, but the speakers were set up as per the SF protocol. The salesmen was a real pro and had been doing this for 30 years. Always a pleasure to work with someone who could teach you and not the other way around.
Don't get me wrong, the Dag was a very fine amp, just different sound. I could see them in a theater situation being fantastic. Gobs of power and plenty of current.
They were using a Mac pre, but did not get the model number. I asked what speaker cables, but being 67 comes with some drawbacks. What you ask, I don't know, I forget!

Jeff

Dealer was Southeaston Systems in Mount Pleasant, SC. Peter Wainright was the contact.
Yes, I spelled the dealer name correctly.LOL

Just a visual comparison sure looks like more than a low rent chassis to me -- the Master Classic transformer is behind the white rear cover. Two totally different designs.

Momentum 400 Top view
https://i.imgur.com/i3EFZja.png

Master Classic top view with massive & heavy amp cards on each side
https://i.imgur.com/t0W4WNF.png

Poor picture -- but side view of the Master Classic amp card
https://i.imgur.com/siH42gO.jpg

Best Sirs,

Bob

Jeff, I would expect that MC275 sounded more natural to your ears. They are designed to work together. Using the MC275 is always hit and miss when combining preamp and amp combos of different manufacturers. due to impedance problems. I have had good luck as have many others using ARC and D'agostino as they have better symmetry when combining tube preamp with solid state amps.

:DWho is the source? Dealer or manufacturer?

Besides the copper and aluminium differences they are different in the fact that the Progression uses a single ended driver stage versus the Momentum's complimentary driver stage. This straight from Bill McKiegan whom I spoke to before replying to this. He did agree with your statement of the Progression being more "traditional" as the Momentum was designed to work and sound fantastic in a compact package. They also have different transformer windings for all three amps. In my opinion the Progression is much closer in sound to the Momentum than the Master Power as it shares some of the ideas trickled down from the Momentum amplifier. The Master Power is the "entry level" (gateway drug)!

On the D’Agostino web site, the Classic 2 and Classic 3 are now listed as discontinued.