, I own original Carver Amazing Loudspeakers, and I recently purchased a used pair of JTR S2s. I have not heard any other JTR speakers. In my opinion, sealed subs, ported subs, and planar subs all have a different sound. As suggested already the different types of bass may not play well together in the same room.
I believe you should stop investing in new equipment (one possible exception below) and instead work on getting the most from what you already have. As a Carver Amazing speaker owner I am sure you know, you cannot just plop them down, connect wires, and expect to get the best sound. An active crossover, like you have done, positioning, different amplifiers all make a difference in sound. Have you tried adding weight to the base of the Carvers? I use some dumbbells I had on hand and it improved the bass. Are the Carvers 5 feet from the wall behind them? Set up properly, the Carvers can fill a large room with very nice bass.
You have some great equipment. Now you can stop spending money and spend time to improve your sound. A friend familiar with REW come over to help me with the S2s. He took the time to make sure all the speakers were working together by time aligning them. I can’t emphasize enough what a difference that process made. It’s like having brand new speakers. The system is louder and clearer in the main listening position. I now listen at a lower volume on the preamp.
I am still adjusting to the new sound and trying to set levels that work for music and home theater. To be honest even with music, I have to adjust levels sometime. Sources do vary in volume and equalization. In my opinion, it is important to know where everything should be adjusted for a flat response as a reference, from there adjust to taste.
I am not familiar with the Marantz. I am using a Sherbourn PT-7030. The Sherbourn preamp allows me to make temporary volume adjustments to any of the 7.1 speakers from the remote. When I change sources, the setting return to default settings. I am also able to adjust sub levels based on what format is playing, 2 channel stereo, various forms of Dolby, etc. I have not set individual levels but that may be the next option I try. It may take months to get your system dialed in. Keep trying, you learn in the process, and the results are well worth it.
By the way, the JTR S2s are flat to 6 Hz in my 14 x 29 x 8 room. The subs are 8 Db down at 5Hz. I currently have them positioned in diagonal corners. I did invest in a Minidsp and if your equipment does not allow you to individually equalize, control the delay, and adjust the volume of each sub I would suggest you invest in one. I ordered the regular 2x4 and it works just fine for my needs. Your room is larger and may require more delay than the 2x4 allows. Stepping up to higher models will allow a greater range of delay.
I apologize for the very long post. Good Luck.