catridge match with Morch DP-6

I would go with the Kontrapunkt B or the new entry level Allearts.

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.

Thanks everybody for the advices. Personally I like the finish and workmanship of the Morch DP-6. The only thing that I am worrying about is those contact points with the swappable arm tube, which is being held tight by a single screw. I wonder if it would have any problem / wear over prolong usage and arm tubes swapping. I guess those guys around which has been using it for years could pass on some info. Thanks.

You should consider the Origin live silver arm with the shelter 501 combo, best value for the money. It uses the same armboard as the Rega.
This combo is hard to beat period. The Origin live silver arm with the shelter 501 is good enough to be used on the best turntables. You will not need better on your current table. What is your phono section? This may need an upgrade also.
good luck,
Ron

the flexibility of the moerch as stated above makes it a potentially good match with a wide variety of cartridges. i have used a dp-6 with excellent results mated to an allaerts mc1b. mine has been rock-steady in it's setup, so i can't account for the experience cited above. also, the appearance belies the structural rigidity of the arm, which is well known. the mechanical coupling of the arm top to the pillar will undoubtedly withstand however many swaps one desires. just wanted to chime in on the "plus side." good luck with your choices!