BEST TONEARM FOR HIGH COMPLIANCE MM

Isn't the cartridge called "XSV4500", not "4000"?  If not, then I have learned something new.  Never heard of the 4000.  You've received several excellent replies to your question; I think they're all good ideas. To add to the data set on the Unitrac, this is also one of Win Tinnon's favorite tonearms.  But what strikes me is that if you own a Moerch, can't you get a second arm tube for it that is medium or low mass, and just go with that?  Might save money and the aggravation of mounting a second tonearm.  And the DP6 with a medium to low mass arm tube will likely be at least the equal of anything else mentioned.

I can second the ADC LMF 2 tonearm. At 8 grams it is low mass but yet built very well and super easy to operate and adjust. I have used it and been very happy with the results. 

4000 was a quadraphonic cart..
with ADC you must be SURE to get all THREE collar weights , only way to adjust tracking force .

All the XSV 3000 through 5000 could be used for quad. They had response to 50K.  I think these came after the 4-ch era and not many cared. The 4500 was XUV not XSV and was a 4-ch cart. These had a quadrahedral tip. The other extended contact tip was stereohedron.

Fleib, I yield to your vast knowledge on these subjects.  I've got a used 4500 somewhere, I think. Never heard it.  I had been under the impression that XSV4500 was in the line with XSV3000, etc.  Now, even as I write this, I am questioning my memory.  I do know the XSV7500 is an analog of the Stanton 980LZS, or no?  What is "U" in XUV?