I've just listened to my copy of Atlantis without orchestra and it works fine as it is. That said, the strings are so much part of my expectation that it sounds a little bare without them. The bass, not recorded at a very high level, is slightly more discernible. But it's rhythmic rather than melodic and I'm not sure it benefits from being more audible.
Interesting, to me, is that Theme For Young Lovers is so sumptuous that the last chord on the original single sounds as if there's an orchestra there: there isn't.
But on stage, and on At Their Very Best, Cliff Hall added strings to it. This is now seen by many as the way to do it.


