OP,
I find Mac has a house sound… well, you put your finger on it. I guess we will find out if you find the Mac tube sound different.
I upgraded my headphone system to an outstanding 300B system (Woo, with top notch Takatsuki 300B tubes) that put my main system to shame… because my main system did not have the warmth and organic musicality of my headphone system. My main system was incredibly detailed… but had lost its musicality. So, a lot of upgrades later my main system now has the warm midrange and musicality of my headphone system… it is highly detailed but incredibly musical. You can see my systems under my ID. To me Audio Research has this perfect combination of music first, but with details and soul that my 300b headphone system has… but not a budget sloppy warm 300B system. The very best of both worlds.