Bio reactor is definetly the way to go for bio.
Mechanical is were opinions differ. Some like socks. Some like pads. I prefer pads to socks due to ease of cleaning. I can clean pads much faster and easier then I can socks. Pads you just hit with a pressure washer and flip wash other side and done. Takes me longer to flip socks inside out then to wash a set of pads.
If I was building a filter now from scratch I'd use stainless screen. I think this would be the mechanical filtration easiest to clean by far. No washing machine or power washer, just a simple rinse.
Incorporate 3 different grades into the sump either horizontally or vertically then go back up to tank, with a lower flow rate pump feeding the reactor OR gravity feed 2 reactors but if I'm not mistaken the reactors need a lower flowrate then what would typically be used on a decenet sized ray tank. I know screen/sump/reactor will be my next filtration of choice.