Sorondo was signed on a free transfer by former manager Iain Dowie, after he was on a season-long loan from Inter under Alan Curbishley. He then suffered a back injury in the opening game of the season against West Ham.
Pouso signed on transfer deadline day in August on a season-long loan from Penarol but played for just 57 minutes against Portsmouth in September.
Also leaving SE7 is the final part of the club's management structure, general manager Andrew Mills. Mills was brought in alongside former managers Dowie and Les Reed to deal with transfers and take some of the pressure off of plc chairman Richard Murray.
But in this season's revolving doors theme, Mills is the third member of the failed management team to have left in 2006-07, which leaves first-team coach Mark Robson as the only man left from pre-season training.