I'm fine recording six shows and playing back two. The problem is iSCSI seems to take whatever network route it pleases and strongly prefers LAN1 on the NAS. Not a problem with one iSCSI Initiator, but will be an issue with two. The NAS has four gigabit LAN ports so I should be able to support up to 3 iSCSI on dedicated NICs.
Without clustering you can't have two connections to one target so you wouldn't be able to share recordings. Outside of creating a share (of the iSCSI target/drive) on PC a and letting PC b access it.