I am currently running active with a set of ID XS65 in the stock door location of my '02 Tahoe on a Zapco ST-4X. While it sounds ok, it is not loud enough for me. I have done zero deadening to the doors thus far, though I did that on purpose so I could hear the difference for myself when I follow the recommendations of Don(SDS) for doing up the doors. I find myself having to dial back the mids to balance things out anyway, which seems odd to me considering the tweeters have a higher sensitivity and are receiving the same power. When I set the gains I had the tweeters crossed at 2.5k with a 24db slope. I played some music and went up til I had a nasty irritation/screech in my ears and backed off a little bit.

I am wondering if raising the xover point to 4k and retuning would get louder before distortion. Also, these particular tweeters have removable grills and I was wondering if it would make an audible difference taking them off since they a also behind the factory door grill as well. Just don't want to take the doors apart more than needed if it's not going to make a difference as I'm looking for a pretty significant volume increase over what I have going on right now.

From the reading I have been doing lately, I am wondering if horns are in my near future.

Location is probably your issue.

I would hold your evaluation until you finish installing them properly (deadening). you could experiment with other tweeter placements/aiming. I use duct seal to stick them different places (a pillars, doors, etc). 

Currently have some of these in my Suburban and feel they get plenty loud although I always felt that the older style 97 suburban had a better on axis response from their factory tweeter location being as they are aimed at an angle towards the driver. 

 

I also have horns some ES pros and USD's to compare them to and there is absolutely no comparison between the 2. Horns just get stupid loud and sound good doing it. If you've thought of switching to horns already then stop hesitating. 

I actually had these in q-logic kicks at first and that actually sounded better. It was also slightly louder but not by much. I played around with the tweeters on the a pillar facing a few different directions and that pulled the stage up(awesome) but it wasn't a whole lot louder than on axis down in the kick. I am considering horns as the consensus here says that multiple drivers is a terrible way to get louder, at least from a quality of sound stand point.