I have a good subwoofer/amp setup but using a line-out converter just doesn't give me the clean sound I want. Are there any type of aftermarket EQ's I could install or anything that would improve the sound quality? I realize that nothing beats using an RCA connection to an aftermarket radio but there has to be something I can do, right? Right now I am using a standard LOC with no processing. Would replacing it with something like this make a big difference in the subwoofer quality? Are there better ones that would sound closer to an RCA connection?

 

You can usually get by with less than a hundred dollar part. What are you using now?