by Bob TarteMedieval philosophy as passion is probably easiest when you're not living in the remnants of centuries-old prejudices and ethnic feuds. Sheer intellectual luxury for an American, one might expect. But commitment to a lost spiritual path strewn with roses, grails and ecstatic souls sings with each string of Shroeder-Sheker's harp and the flute-like transparency of her voice. Vision is the key. And discipline. One would love to hear a tightly wound Robert Fripp work up a sweat in counterpoint, but the chasm between notes of these simple Irish, Romanian and Sephardic hymns is too great to fill with anything but ringing silence.