Makes no difference how you hook them up. High level, RCA, no difference. What you heard:
Also with one its a lot of work to find the best location with the smoothest response. With four they can go almost anywhere and it will still be very smooth and even and articulate.
Bass sounds were level and tight where as before with the one sub sometimes some notes were louder than others. Also the depth and layering of the sound stage seemed to increase.Is normal and expected when adding subs. What you are doing is building a distributed bass array. Do a search. Four is usually optimal although I run five and found that to be better than four. https://systems.audiogon.com/systems/8367
What has been your experience with multiple sub connections and bass integration?My experience is the more subs the easier and better the integration. With just one its like you said, the bass is lumpy. With more its more level and clear and with four its downright holographic what it does to the sound stage.
Also with one its a lot of work to find the best location with the smoothest response. With four they can go almost anywhere and it will still be very smooth and even and articulate.