Before you totally dismiss PlayBuf as @elgiano suggested, wouldn’t using PlayBuf with a demand ar Ugens to move the playhead give you the same precision and control as using BufRd? In any case true sample accuracy in SC if very hard to obtain as UGens introduce a small amount of delay and the exact amount of delay is not obvious, see this post. As far is I know, there is no easy way of detecting and compensating the delay caused by UGens.
Communication between language and a running synth with any kind of buffer playback will make sample accuracy impossible in any case, so once initiated, the synth must be on its own, so to speak.
I personally gave up on trying to hunt for sample accuracy in SC, it made my life better:) Just my 2 cents.