Those Coincidents are small and likely not extended in the bass, which is a good thing for a SET with small speakers. It still might be enough for a small room, depending on expectations. If expectations are to have it all, you could very well end up with a sub in any case in lieu of larger more expensive very high efficiency horns or something along those lines. Just more food for thought. You might not like the idea of adding complexity with a sub, but that price you pay might be small in relation to the benefits of cutting to the chase faster and doing it with the stuff you already like a lot making most of the music.
It wouldn't hurt to pick up a sub used somewhere locally and try. If it does not work, you can sell, loose nothing and be no worse off than currently.
Powered subs are almost always the least expensive way to have it all when needed, with most any speakers or amps. If you can build an amp kit, I suspect you will be able to get the sub mixed in adequately in a reasonably short period of time. I've done it. It can be no more complicated than trial and error with various settings and placements while listening to various reference recordings along teh way. Kinda fun in its own way, just like building the kit. Plus you have the ability to tweak as needed without replacing. Not too shabby!
It wouldn't hurt to pick up a sub used somewhere locally and try. If it does not work, you can sell, loose nothing and be no worse off than currently.
Powered subs are almost always the least expensive way to have it all when needed, with most any speakers or amps. If you can build an amp kit, I suspect you will be able to get the sub mixed in adequately in a reasonably short period of time. I've done it. It can be no more complicated than trial and error with various settings and placements while listening to various reference recordings along teh way. Kinda fun in its own way, just like building the kit. Plus you have the ability to tweak as needed without replacing. Not too shabby!