Ive heard recordings made from vinyl to an Akai GX something? Reel to reel. I know this isn't a Tandberg or Revox, but I didn't think it sounded better than vinyl. I noticed losses, increased hiss, loss of top end, and less bass.
But I know what the OP is talking about. Tape has a certain sound.
I take objection to his assertion that tape sounds "better". I agree it sounds different, but don't agree it's better. Back in the days of tape and before CD, I didn't hear anyone saying a recording of vinyl on tape sounds better than vinyl. To me this assertion is weird. I can understand the OP having his personal preference, as we all do, but I don't agree with it. If he simply asserted that he enjoys the sound of tape, I'd be OK with that.
But, to somewhat answer his question. "What makes tape sound like tape", in my experience from recording live music on it, and recording records and CDs on it, I'd say it's the losses and technical limitations that make it sound like that. Those losses and limitations round off transients and blur sounds together, and this gives a certain sort of sound. I know a guy who has a studio who has on occasion mixed down his multi track digital recordings to tape to get "that" sound as an effect. I agree that it can be a pleasing effect when used artistically. All formats to my ears have a intrinsic sound of thier own. To my ears digital has the most detail and least colourations. Vinyl though pleasant has a lot of resonance and noise when played back - listen on headphones if you want to hear it easily. Tape, is second best to digital, it has a dragging smeared and grainy sound compared to digital. On its own, tape can sound nice.
Any unremasterd CD of tape recorded music (meaning any music recorded from 50's to late 70's) reveals the characteristic sound of tape.
Compare those recordings to any music digitally recorded and the absence of smear, noise, grain and colourations is immediately apparent when hearing the digital recording.