Well, that's why I had to make an exception to my rule(s). Because I have to assume that the Harmonix is a 10 AWG cord even though they don't specify. Personally, I'd write to May Audio and find out. PC manufacturers who don't specify wire size are one of my pet peeves -- because as far as I'm concerned, "energy transfer" is the name of the game with PCs. And AWG size affects a PC's ability to do its job more than any other attribute, with fancy plugs, teflon insulation, shielding, etc., futher down the ladder. If a cord can't transfer the energy back and forth to the component (ESPECIALLY amps) unimpeded, then who cares about all that other stuff?
So much for my rant ;--) I'm assuming your Harmonix cords will be your best (and biggest) cords; and the two components that most benefit from high quality AND big are the amp and the DAC. The preamp needs a high quality cord, but most don't have the kind of energy transfer needs of amps and (shielded for) DACs (there are some people that disagree with me about the DACs, but I don't talk to them anymore ;--) So a good 12 or even (smaller) 14 AWG cord of 1.5m length should be fine, even for a tube preamp (which draws more wattage than a SS.)
The only other place you want big AWG is from the wall to your power device. Fancy is nice, but not critical in that position. Oh BTW, with separates now, you may find you get better sonics with your amp NOT plugged into the Audio Magic, and just into the wall.
I know you're still wondering why DACs should have the same energy transfer requirements as amps. Well, it just plain doesn't make sense, I know. So perhaps the first answer is "they don't." Of course, the next question then would be; So why do DAC's sonics benefit from large conductor size power cords? My guess, and it's only a guess at this point (I really should call Jim Aud at Purist and find out what he thinks ;--) is that the speed at which DAC chips operate PLUS the fact that they generate digital artifacts BACK through their power supply and cord means that a lot of metal in the PC conductors provides for plenty of CLEAN power while still leaving enough "meat" to absorb the (digital) crap going the other way. Just a theory though.