erik_squires"Cool part is when you learn to EQ the bass and realize you can fix your room modes."clearthink:
Right. Clearthink is absolutely correct OP and you would do well to listen.
EQ can not fix, correct, or eliminate room nodes the nodes will always be there all you will do is add distortion and an even more uneven net frequency response plot.
The single most important factor in getting good deep articulate fast and smooth bass response is the number of drivers. The more subs the better. That includes the bass drivers in the full range pair.
The idea of improving the performance of the stereo pair by using a crossover to reduce the load on the amp and speakers, I get that. Its true. The problem is it comes at a cost. Not only the cost of the parts, being much more complex it has to cost more. But also cost in terms of sound quality. If your goal is sound quality that is not the way to go.
What you want to do instead is leave the pre alone and simply add a sub out. The simplest, easiest, and most cost-effective solution is what's called a Line Out Converter or LOC for short. Do a search, you will find them all over.
The LOC is nothing more than 2 resistors per channel. It does nothing more than reduce speaker voltage down to line voltage, ie about 2V. You can see one here done on my Melody tube amp. https://systems.audiogon.com/systems/8367 Scroll down you will see a picture of the actual mod, two resistors per channel, you can even make out the values and copy this if you want. Or if you want a more complete description and circuit diagram go here https://www.epanorama.net/circuits/speaker_to_line.html
Unlike all the other options mentioned so far this one is true high end. It will make the system better- not different, not worse, but actually better. It is easy. And it will cost about $2. The only real questions are do you want it built in like I did, or outside? And how good do you want it to look? Mine is built in because it worked for me but that's the beauty of mods, you can do it your way.