Newbie question-- where to throw my frogskins next?

Hey folks, my first post--

So my new year resolution was to get into vinyl and these past 11 months I've been on an very enjoyable, and thanks to craigslist fairly affordable, audiophile neophyte journey.  I really barely know what I'm doing, but think I've lucked onto a pretty sweet vinyl setup;

AudioTechnica 120 turntable (with their standard cart)
Marantz sr7007 (using pre-outs for front speakers, but built in for surround speakers)
Moscode 300 ($150 craigslist score!)
Klipsch Forte I (replaced crossovers and tweeter diaphragms) 

So my question is, if I wanted to throw about $1000 at this system, where would I actually hear the biggest difference?  Better turntable?  Tube preamp?  Save my money as the difference would be negligible?  

I'd love to find a deal on a Mcintosh preamp, but the truth is I use the system for home theater and gaming and appreciate all the HDMI switching and surround sound the Marantz is giving me.  But I am also listening to vinyl every day now...  :-)

Thanks in advance for any advice!