Need help with phono cartridge selection

If part of your question is how to get proper loading/matching for these cartridges:
1.) The low output should be run with the pre-amp set to the MC position for the phono input.
2.) Most high output MC carts were designed to mimic standard MM carts in terms of output level and load requirements - so try that one with the pre-amps phono input set to MM.
Assuming that your high output MC is actually high output (MM signal levels) - you don't want to run it into a MC input because you'll probably electrically overload the phono input - this will sound really awful. Years ago i had a customer repeatedly bring in his table/arm/cart complaining about mistracking - which we could never reproduce on the service bench setup. Finally visited his home and noticed he was running into a MC input with a high output MC - he thought he was getting more power because he didn't have to turn his V/C up as much in the MC input - but on louder passages the distortion was truly awful because of overloading the input.Switched to MM input and all was well.

Good answer. :)

They both exhibit wonderful sound reproduction.

My post was mainly for obtaining information from folks that have had system experience with the aforementioned products, so I can benefit from that knowledge and properly evaluate the cartridges.

You say you have heard plus and minus'with both cartridges. Neither will have value in the re-sale market.
Therefore the simple solution is KEEP BOTH OF THEM

Retuc01 - charts and graphs mean very little. The cartridge sound is the important consideration. If you like it fine, however, the fact that it is so old is suspicious. Rubber parts deteriorate from ozone in the atmosphere...things harden and soften.... I would have it checked out by Dynavektor..it probably needs a rebuild.

They are late 80's models...but I purchased them recently new in the box. I examined the stylus, cantilever and housing and they are spotless.

There is some blog info out there about the 10A...but precious little on the 20C. The 10A retailed for about $ 390.00 and the 20C was around $ 550.00. They both have very dynamic sound reproduction qualities and I have the orginal spec sheets and independent test metrics. I am just not that knowledgeable about high versus low outputs and their interactions with the equipment I own. The Preamplfier has a MM/MC switch in the rear that is tied to a phono stage in the chassis so I am able to utilize the MC cartridge...but I don't have the paperwork any longer for the Pre so I can compare specs for it against the cartridge.

How old are these carts? I haven't heard of either one. Are they similar in age to your Hafler and Snell (25+ years old)? If so, the rubber suspension has probably deteriorated. I'd have them checked out before using.