Filters do work well if selected properly for what you intend to listen to. That requires some thought. The simplest solution would be an adjustable filter that will do the necessary width without much degrading of sensitivity (one of the trade-offs with filters). Be prepared to spend as much on such a thingy as you probably did for your receiver. They are not common, require a lot of money and preparation for use. To the best of my knowledge, I've never heard anyone I would spend that kind of money on to listen to, sorry 'bout that.
DSP filtering is probably the closest you can get to that variable, one size fit's all, kind of filter. They do have their own qwerks though, so they are seldom -the- best solution for any particular listening problem. They do get 'close' though.
The only recommendation I'd make about filtering/filters is to get them from a company who specializes in them, which is very seldom the manufacturer of the radio. I'm a fan of Kenwood, but have to say that they produce the worst filters I've listened to. I've found that 'Inrad' produces the best filters I think I've listened to. If they make a filter for your particular radio you can bet that it's better than the ones normally supplied by the manufacturer of the radio. It still requires some thought about what their intended use is 'for'. That isn't as simple as it seems.
- 'Doc