Non Rega cartridge suggestions on a P6

My experience is limited, but from memory I believe you would be safe with many Audio Technica cartridges and Ortofon makes a line of low profile cartridges specifically designed for Rega arms.  What you should look for is a low profile in particular.  

Nagaoka, Benz and Dynavector cartridges tend to sound good on the P6. If you experience dust cover issues, the best solution is the Rega 100 gram tungsten weight, which also improves the sound quality of the table. I believe the standard counterweight accomodates cartridges up to 14 grams which should be sufficient for most cartridges that are a good match to the effective mass of the Rega tonearm.

The tungsten weight is mainly needed due to its smaller outer radius…a shim greater than 2mm will cause standard counterweight to hit the dustcover. 
Rega could solve all these issues if they cared to by making their dustcover taller and making their arms height adjustable, but they evidently don’t care. 

I used Hana EL on P2 as per recommendation from Upscale Audio. Give them a call. They know what works on these tables