My 2001 U320 did not come with a head unit for the Bose speakers so I've been trying to come up with solves for a while now. There isn't a ton of good information here on the forum or online so I'm going to do a brain dump of what I've learned. If anyone can make corrections to any of this info please chime in and I'll update it.
Lifestyle 20 vs Lifestyle 30
There are two Lifestyle systems that came in the Unicoaches. The Lifestyle 20 and the Lifestyle 30. While similar, they are not the same nor compatible. I do not know what year they transitioned to the 30 but my 2001 has it and I'm pretty sure they used the 20 into the late 90s. In both cases, the head units are unobtanium these days, which [almost] makes the rest of the system useless because they both use a proprietary cable to communicate to the subwoofer/amp, which in turn powers the speakers via RCA cables. The cable between head unit and subwoofer is different between these two models. The Lifestyle 30 has a 4th pin in the second row of the plug (see attached image).
Replacing the Lifestyle 30
If you do not have a head unit, look at the back of your subwoofer (likely located under your kitchen cabinet drawers) and count the number of pins required. If you have that 4th pin, you are in luck because you can buy the Bose MC1 head unit instead (pictured below). The model number of the sub SHOULD be PS48 iii. The MC1 is a newer head unit that's compatible with that sub/amp and easily found on eBay. I was able to source mine for about $200. At the time of this writing, a full MC1 system with head unit/sub/speakers was going for about $800 despite it's age, so they're well regarded systems.
If you buy the MC1, you'll likely need to piece the parts together from different sellers (ebay). You will need the head unit, a power supply (part# dcs91), and a remote (pictured below). I had the remote from my Lifestyle 30 already and it works perfectly. You do not need the satellite display that originally came with the MC1.
The MC1 does not do anything except receive input so you'll need to come up with your own CD player or Bluetooth receiver that plugs into the unit. Inputs are well labeled on the backside. Audio from your TV can come in via optical or RCA cables. It can be hooked up directly to the AM & FM antenna wires likely already in your cabinet and you can change the station via remote.
By and large I'm pleased with the system after hearing it for the first time in the 2 years that I've owned the coach. Not a ton of mid-range sound but the directional capabilities of all the little speakers makes for an awesome experience when you're sitting in the living room and have them pointed at you from all around. You would be hard pressed to install a better system for less than a couple coach bucks.
Just as a reference point, our 03 has the Bose AV3-2-1 Media Center
Elliott , with the new head unit what if any Bluetooth set up are you using? My lifestyle system works, but display doesn't nor the cd side. So this might be a great setup for me.
This one from Walmart: Robot or human? (https://www.walmart.com/ip/Monster-Bluetooth-Auxiliary-Audio-Receiver-Kit-with-Voice-Control-7-Pieces/643766519)
It works well and is dead simple. My only complaint is that it goes to sleep after inactivity so you need to click a button on it the next time you want to connect.
Another option (what I use) is an Amazon echo with Alexa. It has Bluetooth and internet capabilities as well as an aux out that'll plug into the back of the Bose.
As for the project goes, glad you finally figured it out. The Bose speakers are quite nice to have. My inputs appear to be going out and the left side cuts out every once in awhile. The speakers should be able to be plugged into a new non-Bose receiver. Speaker Wires will need to be run to each of the speakers and the sun may be able to be used with a little wiring changes. That'll be a fun project if I feel I can't repair the sound issues I currently have.
I bought the Amazon Echo Dot for $20 a couple days ago just so we could have something that streams music directly to the Bose system. Good for having company over or when we want a bit of ambient nose for the dogs if we leave them behind.
Hm... like dance parties at 2 am? That sounds fun. For some.