I have been a Slingbox user for multiple models (classic, solo, Pro-HD, 500).
Does you STB require that you use 1080P or HDMI connection to Slingbox? I ask this because broadcast TV are 1080i max resolution and most STB can output 1080i via component.
If so, then I would suggest you to get the Pro-HD or the SOLO (if you're not using multiple inputs) over the 500.
This is because the older models allow you to load custom remote bin files (google "remote bin slingbox").
With the 500, this function is removed and you are pretty much held hostage to whatever remote Slingmedia has on their database. I heard they update their database once a quarter but I never relied on that so I can't say.
I am glad to see you here on the answer forum, I am sorry to see that you are having a problem with the remote that you are getting not changing channels. If I could get a little more information I would be more than happy to help you with the problem you are having. If you could give me the cable box that you are using I could help point you towards a remote that should get you up and going. A few things you could also try are:
Hope these help,
Sling Moderation Team