I think you should get to discover as we did back in 1980 the sonic advances Mac made in their new designs......I am looking forward to your impressions without my specific rememberences from decades ago. Moving magnet type cartridges frequency response can be affected by the capacitance the signal is subjected to most often by the turntables cabling. Mac started adding the capacitance their preamps "showed" the cartridge in the early 80s. I would not worry about it until you have overcome all the really important turntable setup procedures and then you will need a speciality test record and test gear to do anything analytically about it. A standard professional distributed load impedence for professional sound equipment is 600 ohms......Mac is just stating it recognizes this standard with the line out if you would choose to use it with a pro mixer, studio reel to reel or other such non consumer product. Since the line out is seldom used by most end users, they use the main and tape outs so it will not affect your use. If however you would choose to purchase a TOA distribution amp, add a paging microphone to call in the kids for supper and then hang a dozen background ceiling speakers throughout the bar, a narthex, a game room,etc. you can rest assured Mac has you covered with the proper output into that pro amp.