Best Subwoofer Connection for Music

I have struggled to integrate subwoofers into my two channel systems in a way that enhances the system’s musicality. The best system so far is an old, cheap, dual coil subwoofer, but it has limited capability. I have two subs I want to add, one each, to each of my current systems. (Profile still under construction, which I’ll detail below.) I’ve heard PS Audio’s recommendation of the use of high level connections for music (versus low level connection for Home Theater LFE [Low Frequency Effects]), and I caught a comment on one audio YouTube post to be sure your subwoofer had both hi-level IN and Hi-Level OUT. This, to me, means that the subwoofer connection for music being recommended is Amp [Left & Right] —> Subwoofer Input [Left + Right] —> Subwoofer Output [Left & Right, again] —> Main Speakers [Left & Right]. Is this right? Just like the old dual coil subwoofer, but this time, the Subwoofer plate amp is adding Left + Right.

One Sub has both low level and high level inputs [an 90’s RCA 10” 100 Watt unit marketed by RadioShack. The other Sub, 15” 250 Watt from Dayton Audio, has three different options for audio I/O, to include two sets of low level I/O: (1) RCA and Speak-On connectors for low level input, and (2) RCA and XLRs for low level output. Meanwhile, it also has (3) high level spring clip speaker connectors for both input and output.

(1) I would like to integrate the smaller sub into my tube setup which consists of a Rogue Audio RP-9 + Rogue Audio ST-100 Dark 100 wpc feeding a full-range vintage acoustic suspension Warfedale W70E 3-Way which features a wonderful 15” driver, that I sometimes wish had a bit more ‘punch. (2) I would like to integrate the larger sub into my solid state system which features a McIntosh C100 preamp [I’m still learing how to parse McIntosh model numbers] which allows one to connect to three separate amps [Main (unswitched) + Speaker 1 & Speaker 2 (switched)] currently feeding dual McIntosh MC252 power amps bridged to mono, powering 90’s era full range B&W 801M Series 2 speakers with front ports and upgraded crossovers. The B&W speakers could benefit, I feel, from the ‘wrap around’ room-filling bass sound a 15” driver can provide.

The Dayton plate amp is the most recent addition, and if I need to upgrade the plate amp in the old RCA sub, I’m open to that, maybe by Christmas. [I had forgotten it had only ‘one-way’ connections.]

I’m mostly concerned with what connections would allow me most effectively integrate each sub into my two ‘music only’ systems. Thanks for any help you can offer.