I don't know much about reaper, or addictive drums, but you might have better luck posting this question in the reaper forum, and mentioning a few keywords in the title such as "Addictive Drums in Reaper" etc.
The best thing you can do to improve recording quality is to improve RECORDING QUALITY. Look for ways to get a better sound from your kit before you even touch the mixer.
First thing to look at is your kit. Do you have a good kit? Are there certain drums that you can/need to upgrade? Is it tuned properly (can't be stressed enough)? What's your room like? Can you treat it?
How about mics? The mics you use make a huge impact on the sound. Maybe you're using the wrong mics on the wrong drums. For example, instead of using condensers on your overheads and
a dynamic mic on your snare, try the opposite. I've gotten great results from doing that, and I've also gotten better results from doing the opposite on other recordings. Depends on the track, drummer, kit, and room.
THEN, after that, EQ is your friend. Take out what you don't want, add a little that you do. Gating can work if you have too much spill on certain tracks (eg. too much kick in your snare mic).
Compression can be great at tonal shaping (rather than the most common - and not always best - use which is volume levelling). For example, I like to compress the hell out of snares on rock
tracks with a really slow attack (up to 50ms) so that the inital crack cuts through and it turns the rest down. This way, I get more attack from my snare. But then again, it depends on if the snare needs
it in the first place. You could already have the right sound, and end up ruining it with effects.
Then there's stuff like reverb, which I like to put on snares and toms to taste. It's all experimentation til you find the right sound. Don't expect to get it right the first time. You gotta make the crap before
you can make the gold. And you never stop learning.