Here are 2 ways you could monetize your site in an additional, powerful way. (The first one, let's say, grey hat & the second one blackhat, dark as night.)
1. The greyhat option. Add something like this near the download button:
WARNING!
Your IP-Address is <IP-Address>. Downloading songs is illegal and could easily get you a lawsuit, costing your hundreds of dollars or even more.
By instead using <ref link to provider of mp3-flatrate> and paying just $X.XX per month for unlimited downloads, you stay out of trouble & can also be sure to support the artist of your choice, so there will be more of his/her/their songs to download in future!
Avoid getting caught by a greedy lawyer who's behind your hard-earned money... get your MP3-Download-Flatrate today:
===> REF-Link
(Finding out who you are and where you live is easier than you think! All a lawyer would need is your IP address.)
2. The blackhat-version. Every time someone searches for a song, show them this:
WARNING!
Your IP (<IP>) has been logged!
This is your last warning. Our systems tell that you've been into illegal downloading for a long time now. Further illegal downloads will result in copyright lawsuits, which could cost you up to $2.000 each, per song you download.
If you really want to download music non-stop, without limits, we highly recommend to get a mp3-download-flatrate, which is only $X.XX per month, but gives you the right to download as many songs as you want. You can get such a flatrate here:
===> Ref-link
Yours sincerely,
the ICA (Internet Copyright Agency)
Now, that's really blackhat, because you not only lie to your users in term of them being watched, but also created an imaginary alphabet agency. You could twist this by only showing it to recurring users. This way it's much more impressive, inducing way more fear.
Edit:
Damn, sorry. I did not recognize the date.