I recommend large chambered mouthpieces on the old Conns. Some of the modern small chambered pieces (like Selmer Paris metals) tend to run sharp - though the Selmer USA metals might work ok. If you really want to try metal, I recommend Otto Link SuperTone Master or Guy Hawkins - like a 6 facing on either. Vintage large chambered mouthpieces like Dukoff Hollywoods could work great, too, but they sell for a premium. As you are used to hard rubber pieces, you might want to stick with hard rubber, though. Vandoren Jumbo Java mouthpieces give a bold, edgy, sound but they would be far more familiar to your embouchre than going with a metal mpc. A 55 facing on one of those would be a good size to try. I've used the Vandoren Jumbo Java on my old Conns to good avail. I've got a 55 and will soon have a 75 - not sure which one I'll want as my keeper. Those are great pieces you've got to begin with!

I was lucky enough to own a 10m in years past. I used an old Link refaced to a rather large tip opening for most of the time and it was quite a sound. A bit of work to get altissimo, but that was the facing. I also used a Berg 110/2 which was killer, too, and in tune. Gotta agree, big, open mouthpiece compliments big sounding horn. Anyone have thoughts about what to use with a 6m?