My Akai R2R plays all four channels in one direction, but I never ran across a commercial tape in that format. Were many albums released that way? I never really looked though because until home theater, I had no way to play surround.
Yes absolutely, I wouldn't say many but there's (or at least there was at one time) a number of great sounding Q4 conversions out there (Moody Blues Quads, Doobies Quads, America, Allman Brothers, Black Sabbath, Deep Purple, Alice Cooper, Bread, Doors, Bette Midler, Al Green, Jethro Tull, etc..) among them there was an Aretha Franklin Best Of Quad from consumer reel to DVD-A (Romanotrax?) for example, which was right up there with the commercially released Quadio DVD imho.