Denon DL-103 Compatibility

Where did you hear that? The ideal resonance frequency is between 8-12hz. That arm and cartridge is 13hz. That's pretty damn good!

I have the 103 mounted on a Grace 707 arm. Sounds fine to me! The lighter the arm the higher the resonant frequency of the cartridge suspension/arm mass. The heavier the arm the lower the resonance.

I have the ZU Audio modified DL103 and it sounds fantastic on my Technics SL1200G.  It didn’t sound good on the VPI prime with unipivot 3D arm.  

To any of the above, try a high quality heavier headshell, like the Ortofon LH9000 or the AV101 Orsonic, and I think you’ll realize an improvement, even though you’re presently satisfied. It’s not only about the resonant frequency equation.