Ah... some of the "problem" was from (dev/scsipi/cd.c, cdstrategy):

        /*
         * Do bounds checking, adjust transfer. if error, process.
         * If end of partition, just return.
         */
        if (CDPART(bp->b_dev) != RAW_PART &&
            bounds_check_with_label(bp, lp,
            (cd->flags & (CDF_WLABEL|CDF_LABELLING)) != 0) <= 0)
                goto done;

Note the check for whether we are using RAW_PART.  Using the non-raw 
partitions (/dev/rcd0a, /dev/rcd1a) seems to make pax happy when reading.

	Sean.