Hey Bastie, we may have talked about this before. But, how do you have your TT placed? I remember you writing that your space was limited so it wasnt as ideal as you would like. I used to have the same problem that drove me mad. And mine phono-pre has subsonic filter 18dbs around 18hz. First thing I can tell you is that you have to try alot of different setup and be patient. I almost gave up on records because of that problem. Once you get it right, you will never think CDs sound better than LPs.
First, do you have an access to a carteudge alignment tool? Something like this? http://turntablebasics.com/ It's only $20(US). If you dont have it aligned correctly, you are damaging your cartridge and most importantly your precious and sometime irreplacable records. Also if your cart is dragging on the record surface ALOT more than it's supposed to, it can creat vibration issues. That could be your problem. Whether your cart is setup correctly or not, if you dont have one you should get it before you make anymore record purchase.
Also, have you have a chance to acquire some brass cones? You can get them for about $4 a piece. This is the cheapest website I could find. http://www.madisound.com/cgi-bin/ind...%CArt_id%25%25 I guess one way to see if you need brass cones would be to see if you problem gets worst when you walk around your TT. It could be external vibration that's causing it.
If I looked up the right one you have really nice integrated amp. I say this because I was going to recommend you get a phono-pre for under your budget.
Only Subsonic Filter I've seen is http://www.kabusa.com/index_pp.htm but it costs $170. As I said my phono-pre has good sub-s filter, but I couldn't get rid of it until I move it around. Just make sure whatever your TT is sitting on is heavy and solid. If not, try using a REALLY heavy table somewhere from your house and see if that'll work.
I wouldnt spending your hard earned cash on a sub-sonic filter yet.


Best luck to you.

-JRA