Litter training an entire male is possible, Harvey is approx 8yrs and lives in the conservatory with the other 6 buns. He's faultless, yes we have the "rabbit currants" but even the neutered ones do them to mark their territory.
The easiest way I found was see which corner they preferred and put the litter tray there with soiled litter in, i emptied it every other day and repeated the process but didn't scrub it, just wiped it, that way the rabbits scent is stronger.
A pair of my buns do have 2 litter trays, there big one and a smaller kittten one as they just seem to like weeing in the other corner, tried everything but gave up and just put another one in!