THX Certification is not so much awarded as it is purchased. An audio company must pay the THX group a lot of money to have them "test" their equipment for certification. THX certification should never be the reason you choose a stereo component because many components might be of the quality to be certified but the company did not choose to pay the money.

The reason THX equipment is so expensive is because of the cost of certification.

That said, thee difference between THX and non-THX equipment can vary greatly, and depending on the two pieces, the difference can be negligible or can favor either the non-THX or the THX equipment depending on the quality of both.