Injuries to Jamie Smith (shoulder girdle/rib) and Darren Cave (hamstring) rule them out of contention and they are replaced by David McIlwaine at full-back and Ian Whitten at centre.
The game will mark McIlwaine's full Heineken Cup debut, while Whitten comes in for his fifth appearance at this level.
Up front, BJ Botha's return to fitness sees him take up the tighthead berth with Tom Court switching to the loosehead side of the scrum.
In the back row, Stephen Ferris is set for his first game since picking up shoulder and rib injuries last month. The 25-year-old will start at openside flanker, with Chris Henry dropping to the replacements bench.
"I can't wait to get out there and represent Ulster in such an important game," said Ferris, who was ever-present for the province in last season's pool stages.
"It's been tough missing the past few weeks, particularly the match against Aironi where there was quite a lot of open play and after that I'm really champing at the bit to get going again.
"I think we'll see a big 'pack against pack' battle on Sunday, and I feel that the game will be won and lost up front.
"Biarritz don't like to play too much rugby, when they do get front-foot ball it's because of their forwards - that's where it's all going to start for them.
"We will be facing a very good, tough back row and we'll really have to dig in. But we're every bit the match for Biarritz and I'm looking forward to the contest."
Amongst the replacements for Ulster, Andi Kyriacou provides cover at hooker, Bryan Young and Paddy McAllister are the prop replacements, while Nevin Spence and Irish-qualified Australian Adam D'Arcy, two potential Heineken Cup debutants, cover the three-quarter positions.
ULSTER (v Biarritz Olympique): David McIlwaine; Andrew Trimble, Ian Whitten, Paddy Wallace, Simon Danielli; Ian Humphreys, Ruan Pienaar; Tom Court, Rory Best (capt), BJ Botha, Johann Muller, Tim Barker, Pedrie Wannenburg, Stephen Ferris, Robbie Diack.
Replacements: Andi Kyriacou, Paddy McAllister, Bryan Young, Dan Tuohy, Chris Henry, Paul Marshall, Nevin Spence, Adam D'Arcy.