i owned a z5300 and if what they say is true, all logitech systems share the bloody noisy bass. i cant imagine you even thinking of adding more bass! 

anyway, the 'THX Certified' is just pure nonsense. it means nothing

edit: i forgot to tell you, you basically paid logitech who paid Lucasarts for the cert. the THX cert is a waste of money too, though we cant choose wheter to have it or not