That top of the line Frank has seems very enticing. It's hard for me to pull the trigger as I'd need to spend money when I shouldn't right now and I'm not positive it would be what I want. The amp I use now is truly very good and although the old Hafler is old it looks like new inside as it sat for quite a few years. The sound of the Hafler isn't quite as good as I'd like but still better than I would have thought after comparing it to other amps. If someone wants to send me a 550 I'd pay shipping both ways and a rental fee for a couple of weeks.
I had Frank put MosFET C circuits in my Hafler DH-220. There was a large difference in the sound. Bass was improved _a lot_, and the treble became much more detailed and clear without being harsh. I later had the upgrade to the OmegaStar circuits done and I now have an excellent amplifier that's better than most of what I've heard from other companies (and for not much money at all).
Sheet metal and heat sinks don't really wear out, and Hafler used very good power transformers. The current OmegaStar EX replaces the output devices, so most everything is replaced by new parts. The capacitors in the power supply go after a while, but that probably isn't a concern with a newer amp like the XL 600. (My amp has an AVA-designed board housing a bunch of smaller caps, so it has more capacitance than a stock Hafler. AVA no longer supplies that board AFAIK, so I guess the stock soup can caps work well enough with the newer AVA circuitry.)
Ed Gately and Erno Borbely at Hafler got very good results. It doesn't surprise me at all that your XL 600 compares favorably with a lot of the stuff out there. Some engineers are very good at assembling pieces parts, and others also have real talent. I think the audio industry could use more talented engineers. (Hell, I could probably cobble together amps and preamps using a more or less cookbook approach, and I'm not even an engineer.)
Some of the current computer software probably makes it easier to get equipment that "works." The software will, to some extent, do the work for you. Of course, it also allows a talented engineer to play with and model lots of variations, so they can come up with exactly what they want in a short time. It also allows them to dig deeply into the circuit and get the best performance. Speakers are a good example of the former. You can get software where you just plug in the numbers and out pop the results. You don't even have to understand the math or the relationships between the different variables.
Another concern I have is that you can't change the power cords on these amps and I wonder if Frank realizes what gauge of wire to use.
I think he's capable of insuring that the power cord is suitable. Also, please note that AVA equipment has a good power supply, so you're not going to improve things with a tweako power cord. The differences between various speaker cables and ICs is vanishingly small, especially when you consider how much you can spend on them. The difference between power cords is orders of magnitude less since they're before the power supply and not at all in the signal path. Plus, they're only the last link in the chain from the power company, and the power company doesn't use tweako wire.
