The "free sample" is a good start to the problem.
I often listen to Music Match Radio.
It's free for 1 hour.
It's not bad.
I could pay to have unlimited Music Match Radio, but they benefit from me by listening, liking the music, and buying it at the store. It's like regular radio - it's free, and you don't have to pay a thing, nor are shamed into it. Channel 2, MPR, etc., I donate to because I like what they have to offer. It shows all sides of all issues, is intelligent, and something that I want to maintain on the airwaves.
But MusicMatch? Well, it's Radio, and I can log on to live365 and listen to anything anywhere anytime for free. I can log on to Windows Media Player and listen for free.
If I want special services I can pay. But I don't want them, so I don't.
So, you could make TOL only postable for 1 hour per day.
You could make it subscriber only.
Live365 has listening capacity. If you subscribe, you can get in any station, but it caps for non-subscribers, and you have to wait for someone to leave.
Just ideas. Hope it helps.