I have used Optrix in the past, but stopped using it after it ruined a few disc surfaces - it left a haze on the surface that could not be removed. I could not say it improved the sound at all. I have used Liquid Resolution and that did improve the sound quite a bit by resulting in smoother, more open sound (less digital sounding). I would stay away from Optrix!
Something else that will improve the sound of CD's is to use a tape deck head demagnetizer on them. Turn on the demagnetizer, then slowly move it toward the disc to about an inch away. Move it around the disc in a spiral for about 10 seconds, then slowly back it away before shutting it off. This really does have a positive effect on sound quality, but don't ask why. I use a TEAC demagnetizer that I bought back in the seventies.
Something else that will improve the sound of CD's is to use a tape deck head demagnetizer on them. Turn on the demagnetizer, then slowly move it toward the disc to about an inch away. Move it around the disc in a spiral for about 10 seconds, then slowly back it away before shutting it off. This really does have a positive effect on sound quality, but don't ask why. I use a TEAC demagnetizer that I bought back in the seventies.