It's going to be difficult to find a threaded barrel for that P6... I've only seen one P6 that was threaded to accept a suppressor, and I think that was a custom barrel. Typically Sigs will suppress a little bit better, but between a choice of a P6 and a Glock, I'd recommend you suppress the Glock. You can pick up a Lone Wolf barrel for probably less than half of what you'd have to pay for a Sig barrel, even if you could find a production run.
For comparison, I'm waiting on a suppressor for my Sig 228 right now and have been trying to find a threaded barrel for it. I've been looking for at least 2 months and am having a very hard time finding anything other than a Jarvis or Bar-Sto that would cost almost as much as I paid for the gun (bought it used) and still be backordered. And this is on a gun that a number of people suppress.
For budget 9mm suppressors, you may want to take a look at Thompson Machine. I'm waiting on a Poseidon which is a micro suppressor that is wet and wiped. Basically its a 4" can that meters about the same as a full sized can for the first few mags or so before you have to replace the wipes. TM also has the Isis which is a full sized can that doesn't need to be wet/wiped. And AAC has the Eco-9 which is a very good value. Basically it uses the last generation Evo-9 baffles, and even has an extra so its a bit quieter. The only issue is that it's been discontinued, so it will be more difficult to find. The Eco and the Isis both require a booster, but the Poseidon is light enough that it doesn't require one. All of these run around $350 or so.
