You're taste is exactly the same as mine, and I have the same problem. I have found that Xing, Winamp, and Poweramp all have this limit. Does anyone know of an app without the 300 song limit? If I wanted a 3000 song limit, I could just listen to music on my 3DS...Like I said, my music tastes mean that's unlikely.
They'll probably have all the alternative, dance, and movie soundtrack albums in my collection. That amounts to about a dozen albums out of 300. The rest comes from Squaresoft, Nintendo, or a variety of anime soundtracks. Not the best taste in music, I know, but it also means that the grand majority of my collection probably doesn't fall under Rhapsody's library.