We present simultaneous high time resolution (1-10 Hz) X-ray and optical observations of the persistent LMXBs Sco X-l and V801 Ara( = 4 U 1636-536). In the case of Sco X-l we find that the Bowen/HeII emission lags the X-ray light-curves with a light travel time of ~11-16 s which is consistent with reprocessing in the donor star. We also present the detection of three correlated X-ray/optical bursts in V801 ara. Although this latter project is still in progress, our preliminary results obtained by subtracting the Continuum light-curve from the Bowen/HeII data provide evidence of orbital phase dependent echoes from the companion star.