It looks like the problem was solved with the U24, but for the sake of completeness, I don't think the above question was answered. You can split the tape monitor "out" with Y splitter cables all you want to feed all of the tape decks for recording. The tape monitor "in" cannot be safely split; however, you can use any input you want to play back any tape deck. The tape monitor input is useful when you have a 3-head deck because it allows you to listen to what the recorded tape sounds like while it's recording (and to flip back to the original signal for comparison). But for just playback, any input like "Aux" will work. Unfortunately, vintage receivers typically don't have that many inputs, but the single 8 or 4 RCA switch posted would work fine for playback.
I have the feeling you were saying the same thing about "tape" not too long ago
You might want to start the search for a multi-input phono preamp now



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Possible serving suggestion (Centrex "by Pioneer"):