Northampton, who lost 17-8 at Biarritz in the final pool match, face a tough rematch with the French team in the Heineken Cup quarter-finals.
Eight teams are now in the running for the Heineken Cup
Wasps' reward for topping Pool One is a home tie against Pool Two winners Leinster, and Cup holders Munster must travel to Pool Five winners Llanelli.
The remaining tie sees a rematch of the 2001 final, as two-time winners Leicester host Stade Francais.
The matches will be played on the weekend of 30 March-1 April.
Wasps produced a gritty performance to win away at Castres in the south west of France.
Tom Voyce scored the only try as Wasps won 16-13 and their reward for topping the group is a home tie against Leinster.
Perpignan finished second in the group after thrashing Treviso 45-25.
Leinster mave have won the group but face a trip to Wasps after going down 19-13 in dreadful conditions at Gloucester in their final game.
The Irish side finished on 21 points, which was not enough to earn them a home draw.
In the other game, Edinburgh lost 19-7 to Agen in a dead-rubber contest at Murrayfield.
The Ospreys finished with an 18-7 win at Sale but their draw against Stade Francais always looked like being costly and so it proved.
As expected the French side hammered Italian whipping boys Calvisano 47-6 to top the group on Saturday.
They will be looking for revenge for their 2001 Cup final loss to Leicester when they travel to England to take on the Tigers.
The Ospreys finished second in the group, but failed to progress.
Leicester's shock win at Cup holders Munster means they win the group and with it a home tie against Stade Francais.
The Tigers' 13-6 victory was the first time Munster had been beaten at Thomond Park in the competition.
Reigning champions Munster were already in the last eight and now face a trip to Wales to take on Llanelli.
Llanelli Scarlets finished the group stage on a high as they beat London Irish 20-16 in their final game on Sunday.
Six wins out of six group games means they finished top of the group and they will feel full of confidence as they take on Cup holders Munster.
Toulouse secured second spot, but no place in the knockout stage.
Northampton and Biarritz met in the final pool match at Franklin's Gardens knowing that they were both already through, but with first place in the group still at stake.
After a lacklustre first-half display, Biarritz cruised to a 17-8 win to advance with a 100% record.
Having lost to them twice already in the pool stage, the Saints will have their work cut out in the quarter-finals as they travel to face them for a third time.
Overmach Parma ensured the three Italian sides in the event did not leave empty-handed, registering their first win in the their final pool game against Scottish side Borders.