I think the best price will usually come directly from the pool, since if it wasn't some automated arbitrage bot would probably pick up the difference pretty quickly, so your best bet would probably be swapping 'roughly half' of the hive amount into the PLN pool.
That being said, some more engine market orders should probably be added for convenience if nothing else. The other ones expired based on very outdated engine code that auto-deletes any buy/sell order after a few weeks passed, which by the way, is literal insanity if higher liquidity is the goal, but what do I know... sorry for the slow response, btw.