Tasos, can you describe what happens to the sound of your system when you use different settings on your MIT cables? I wanted to ask about that during the visit, but forgot. I think you mentioned that you now use the lowest setting. If this is the case, and you prefer that setting for sonic reasons, why do you think MIT has the higher settings?
The sound gets edgy with the HD setting, and timbre is affected; it only takes a few seconds to tell. I've been on SD for years, ever since the resolution got high enough.
I would consider Spectral, but I don't like having to commit to a specific cable manufacturer. Also, the brand seems to have a very strong following, but one must commit to their dealer network which basically means full retail pricing and little flexibility. The other concern is that their older models were once described as being excellent, but they existed only to be replaced fairly quickly with newer models which seem to have improved quite a bit in terms of noise and power. I remember very specifically when Goodwins tried to sell me the 360 only a few years ago as the latest and greatest, and I think you said they could not control your speaker load. The new 500s are obviously a much improved design.
If you don't believe in system design, then forget about Spectral, FM Acoustics, Constellation, or Boulder - they all match with and/or require specific cables (and with the exception of FMA, all others are made by MIT; FMA requires you to buy theirs, be it speaker cables, phono cables, or other). The MIT cables are required for a number of technical reasons discussed over the years, since the amps are unfiltered wide-bandwidth designs (so is Constellation, BTW) - see numerous emails I've sent you on this. If you do not appreciate the technical reasons for cable matching, then steer clear.
People may like other cables, but the equipment will not sound right. It's a non-winning fight. If I were you, as discussed a few times in the past, I'd be more concerned about the stabilizing output inductors in your amps (and so many others), than which cables work with Spectral; ditto for the input capacitors in your amps, which you removed (a good thing).
Regarding full retail price, you are looking at it the wrong way in this case: the margins are very low, and the dealer actually pays for shipping as well. The equipment is low to limited production, and the waits very long. No one's going to give you a break.
Regarding the latest and greatest, forget about what the dealer says, of course he would try to sell anything to you; your ears are the judge. You need to bring any equipment home and tell for yourself, like you do with your Pass. Shaping an opinion based on what you read around the 'net or hear at my place, for example, may not be the right way to do it; for example, you mentioned how soft the Drum record sounded when I had the 360s in here... well, I can tell you, it was the arm and noise around the system more than the amps. By contrast, I had written years ago here at WBF about how well the 360s drove the Q7s at the dealer's... they did have a euphonic sound to a certain extent, and the bass was overripe, no disagreement there.
Years ago, I made a request to Spectral (and I am sure I was not the only one, and hopefully it did reach the product owner), which appears to have materialized: "give us the recording," and leave the soup making to others.