PSG was indeed able to pass the last 16 stage to advance to the next round even though the second leg match was at home to Real Sociedad. However, what needs to be seen here is that the level of difficulty for PSG must be there to get through all of this because there is no easy way in the Champions League to get through round after round. I think Real Sociedad will continue to show their skills in the second leg when they host PSG even though Real Sociedad was two goals behind in the first leg.
Most likely socidad may not be able to get pass this stage of the champions league because they are been faves by a team thats way superior than they are and this includes both in strength, form and depth so their chances around Real Madrid continues to be slim and such that they are most likely to not succeed or get pass this stage but then Real Madrid wouldn't and shouldn't take them for granted so they don't get to make qualifications turn out too difficult for them much more than it should have been normally, as the first leg was a huge success then most definitely the second leg which will happen to be their last shot, they will be giving only but the best to make sure they stay ahead and proceed unto the next stage of the champions league.
Beyond this stage I think Madrid may gradually beginning to face more tough and serious teams because so far it's been looking much like an easy game for them but they will soon get to where it will become more of a fierce battle as the trophy is been contended for even by the current defending champions who are willing to make sure they aswell get back the trophy this season again.