The Morch DP-6 is Dual bearing tonearm is way better than the Rega 300B. All the cartridges you mention should work fine with it provided you match the proper Morch arm tube to their weight. There are 4 arm tubes to choose from Light 3.8g, Medium 5.7g, Heavy 7.4g Extra Heavy 13.1g.
As far as the counter weights going out of adjustment they are held by orings which must of been worn out on the Morch arm mentioned. I have had mine for 7 years on a Sota Sapphire with no such problem. I am using a low output Benz Scheu catridge.
As far as the counter weights going out of adjustment they are held by orings which must of been worn out on the Morch arm mentioned. I have had mine for 7 years on a Sota Sapphire with no such problem. I am using a low output Benz Scheu catridge.