I have the other high-profile Japanese direct drive turntable (Technics SL1210 M5G) with the same cartridge you have--Denon DL-160.
But I have done so many things over the stock rig, none expensive or intrusive, that I feel that I have moved it up to the next level. It certainly has more linearity, clarity, dynamic range, detail, and frequency extension than the same turntable with stock mat and headshell, sitting on a typical rack.
Here are the tweaks I've performed; most of them you can do too. Each noticeably improved the sound enough for my wife to notice; taken together they have moved its performance "to the next level."
1. Turntable mat: I replaced the stock rubber mat with a used Oracle Groove Isolator. It's sorbothane, but not sorbothane gel. On top of it I have placed another very thin mat made of polypropylene mesh marketed for drawer/shelf liner sold at drug stores and Home Depot. Lower noise floor; more clarity. The poly mat on top adds slam and sharpens leading transients. You might not be able to find a used Groove Isolator. For new products, the Herbie's and Iron Audio are highly regarded by Technics owners on A-gon.
2. Sumiko headshell: far more rigid, has much better wires, and azimuth adjustment. Rigidity and better wires improved clarity and low level detail; adjusting azimuth does wonders for stereo separation, soundstage, and imaging.
3. Placed turntable on an isolation platform. I used a 1.5" thick butcher block cutting board from Ikea for $25. You can get a thicker one by Cuisinart from Lowe's for $50. There are much better, such as the 2" or 4" solid old growth maple slabs available from Mapleshade. Placed shock absorbing feet under the cutting board. I used Vibrapods; Mapleshade's Isoblocks are highly regarded. Resulted in much better inner clarity, overall musicality, dynamics, smoothness, you name it. Wife noticed the difference immediately.
4. Replaced stock turntable feet with brass cones from Parts Express ($20/set of four). If you want better, try Mapleshade brass heavyfeet. Do your stock feet unscrew? If so, there's a good chance the thread size is M6. You can get M6 threaded Heavyfeet. The brass cones from Parts Express also include M6 threads. Another alternative might be the Isonoe footers available from www.kabusa.com. They also have built-in M6 threads.
5. Added KAB's fluid damper. I know this was made specifically for the Technics, but I think it would be worth a call to Kevin there to see if by any chance it would also fit the Denon. Probably not, but worth a call. Lowered noise floor, improved trackability, less hash and more music in the treble.
6. Record clamp. There are many at many prices. I use the cheapest in existence--the rubber scrunch-on clamp fro KAB for $24.95 (without built-in bubble level). It adds bass and weight to thin LPs, lowers overall noise floor and in particular diminishes perception of surface noise.
7. Remember the polypropylene from #1? I took a couple of 1/2" x 1" strips and scotch-taped them as damping rings around the tonearm, one just behind the headshell, and the other about 60% down the long straight part of the tonearm. I purposely didn't put it in the exact middle to break up resonant nodes. This has a similar sonic effect to the fluid damper--lowers noise floor, adds some quiet space around the notes, etc. Originally wound a 12" strip in a spiral around the entire length of the arm, but that overdamped it and made the music sound muted and uninvolving.
If you do all of the above (or all but the fluid damper), it will take your turntable performance to the next level. Move up to one of the highly regarded cartridges on this thread and you'll move up more yet.
And you'll retain the spot-on speed, bulletproof construction, and silky operation that makes the Denon DP-500M so seductive to use.
