Saracens will host Gavin Henson's Ospreys, while Irish take on Perpignan at the Madejski Stadium and Gloucester take on 2006 European champions Munster at the Kingsholm Stadium.
The quarter-final picture is completed by Cardiff Blues visiting three-time European champions Toulouse.
The ties are to be played on April 4, 5 and 6.
Pool Four winners Saracens can look forward to a dress rehearsal against the Ospreys on March 22, when they meet the Welsh side in this season's EDF Energy Cup semi-finals at the Millennium Stadium.
The Ospreys qualified, along with Perpignan, as a best runner-up after beating French hosts Bourgoin 28-14 in their final Pool Two game.
Irish, Pool One top dogs, face a swift rematch against Perpignan.
The teams have already met twice this term in their qualifying section, with both games being won by the home side.