^Keith, I agree with much of your post and appreciate the effort you put into it. I wanted to do a level-matched BAB prior to purchase but circumstances didn't permit.
But allow me to point out that I fully expected the Emo to sound better than the AVR4310 int amps in the case of the 4310-and in a nonblind A/B/A it "did", but the diff was a lack of distortion and maintenance of dynamics at volume. That made sense to me as the 4310 was just overtaxed with my Dalis. Despite the 4311's int amps being rated to 4 ohms I had my doubts and really expected the Emo to sound better than the AVR, maybe not quite as much, but better. But it "did not". I was surprised and impressed with the 4311's amps. Because of that experience and the many things I'd read similar to several of the points you made above, I was quite skeptical and really did not expect the Halcro to sound better than the Emo. I don't mean to represent that my lack of conscious expectation bias proves anything. I could well be mistaken as to SQ difference, but I was really surprised at the sound of the Halcro. And hesitant to post about it prior to a BAB.
I still intend to do a BAB when I can arrange a willing and qualified assistant. If it turns out that I can't tell the diff, then I could easily sell the Halcro. The good thing about getting such good deals on used gear in exc cond is that I've never had a problem unloading it. In fact, I usually can manage a slight profit.
Hi SoM... nice to have you back from the 'real life' stuff that's been keeping you away from the important stuff :)
I'd expect the 4311 to sound as good as the Emo amp - in fact I'd expect them to sound as good as each other - ie no difference at all. Unless the 4311 was having a problem driving the speakers to the levels required or coping with the load the speakers are presenting. When I got my first Emo amp I had an Onkyo 5007 AVR which was their flagship at the time. I’d say the amps in it would be on a par with the 4311's - that is, good amps. But I also had at that time some speakers that were 4 ohm, that dipped to about 2 ohm at some frequencies and that were also pretty inefficient - and my 5007 just couldn't hack it. The XPA-3 made a very clear audible difference at high SPLs - for all the scientifically based reasons we'd expect. I'd also have expected the 4310 amp to sound as good as the 4311 and as good as the Emo IF it had been working within its design parameters. I am not one of those who say "all amps sound the same" - what I say is that all modern well-designed amps sound the same so long as they are working within their design parameters.
It would be awesome if you could get the rig and the switch required to do a blind ABX test with the Halcro and the Emo, with proper 0.5dB level matching etc - but it is real hard to arrange. Meanwhile, there is only one thing that matters: what it sounds like to you. And from what you say you are more than happy! Like I said to those clients, over and over, perception is reality. So if you perceive it as betterm then it IS better. As you can guess, I am sceptical;) Unless there is a good reason for the Emo not working within its design parameters which I am unaware of.
I also think your model of buying top quality gear on the previously-owned market is fantastic. I wish I could do the same - it would be my sole model too - but over here there just isn’t the market for this sort of gear that you have in the USA, unfortunately. We have a lot of 'audiophile' (read 'overpriced') gear and a lot of 'entry level' gear on sale and that is about it. I have sourced a lot of my gear in the US but the 20% duty we have to add and the cost of carriage usually makes it prohibitively costly. In fact, thinking about it, my entire system is more or less US - Emo amps, Oppo BD player, M&K speakers, SVS subs... I am currently lusting after a pair of Seaton Submersives - but the cost of carriage and the duty horrifies me. Fortunately, Mark doesn't have a 240v version of the latest Submersives available yet, so it's a decision that is easy to delay ;)