First off, audio and acoustics aren't my area of expertise so to speak so forgive me if I seem a bit slow on the issues of sound but I am looking for a decently powerful but clear set of speakers. The only real qualification is that it needs to be 5.1 and that it should cost no more then 100$ USD. I was considering the Logitech x540's although they are no longer produced and not always readily available (plus I should see what the community has to say about them). I also considered the Logitech z506's but many consider it to be a downgrade to the x540's so I just figured that a second opinion should be in order. Any help would be appreciated and thank you.
in terms of sound quality the x540 may be slightly better. i had the x530 and while they do sound a bit better than the new speakers its not by a huge margin at all.
the subwoofer is better on the z506 than the x540 though.
it can be quite hard finding "brand new in box" x540's for cheap. none on ebay and amazon is at $200. you can find them used but for cheap speakers like this i wouldnt go that route. z506 on the other hand can be found for $60-70
for a budget of $100 and a mandatory 5.1 there is only so much you can do... i think the z506 should be sufficient for your needs. its not going to win any awards but if you wanted something high class you would have a higher budget.