transaction search on Opportunities, with PO reference exposed

Hello there, another tricky one and suspect it's because i'm in a transaction search with Opportunity as type, but worth asking. I've built a Saas report for all Opps, both Order Received and Open Opps, so we can keep track of renewals etc. It's working well but would very much like to be able to pull in the relevant PO on those Opps that have gone Order Received, i'd be grateful if you could advise as to how i could do this, the search is grouped by manufacturer and total sell with a drill down showing all items, relevant opp