If you have the surround sound option, which you probably do if you have built in speakers. You should have a subwoofer and 5 satellite speakers, two in the front 3 in the back. Our 07 190 had the same.
The 12v wiring is probably red positive, with green ground, and white or yellow negative, but you will need to check all that with a meter to a 12 source from the battery or inverter section. There probably are not any drawings available unless somebody made one and Roadtrek changed stuff a lot.
The big bundle of small wires is likely for the speakers and it probably goes, or used to go to, and rotary switch that selected vehicle radio or surround sound unit. It is a multipole, probably about 8-10 poles stack in the back and the wiring is horrendous to do. Add that the wiring may be incorrect, or 190 was wrong, Roadtrek admitted they went out bad, but they would not give me a wiring diagram. The said to to the dealer, who said they can't get a diagram either and Roadtrek wouldn't pay as many hours as it would take to figure out. I spent a week testing to get it right then found it had a bad ground on one of the front speakers so I had to take the tray above the driver door out to find it and fix it. Of course then the junk surround sound/dvd player died shortly after that so we replaced it with another brand.
We did put in a 12v TV for a while with a voltage stabilizer, but good ones are hard to find and new AC TVs aren't native 12v anymore so can't just cut off the wall brick any longer on most. We also had a 12v DVD player and there also very few good ones now so they last only a year or two.
I finally did a bunch of power use tests, some are in discussions here on the forum and discovered that you can use an AC TV that has low power use with a small inverter and and actually use the same, or less, power than you do with a 12v TV on a voltage stabilizer. It also gave us the option of using a 110v home Blu Ray player that also has USB input if we wanted, but we went with just plain BluRay that had very low power use as we already had a USB adapter to feed the TV directly. We ran it through the surround sound for a while but the amp unit is AC only and very power hungry. We now use a nice soundbar direct off the TV that is AC powered. All the AC stuff is powered through a 340(?) watt very efficient inverter in the same cabinet.
You will probably have a very hard time finding a replacement unit of the same style as Roadtrek used. We did find one about 5 years ago but it was difficult. The only stuff that fit was from the old dorm room style 5 speaker small surround sound systems that they don't make anymore. I have the one I removed when we went AC only sitting and waiting for me to take it to recycling if you want it. I don't know if I still have the multiposition rotary switch or not, but probably not.
In my opinion, you would be time, money, and frustration if you either use the surround sound speakers from another source but I don't know if you could do that without an AC unit to drive them all and then you have to have that on the big, inefficient Tripplite in the van or an added one. IMO, the speakers weren't all that great anyway and they can't place them for real surround sound in that space either.
If you are looking to be more efficient in battery use, which is likely because you want 12v TV, using the surround sound shoots that down, I think, as it will use lots of power.
A small 110v system with TV, DVD, and a sound bar running on a small inverter would use a tiny fraction of the power the surround sound on the Tripplite would use when not plugged in.
We have had pretty much all the other options at one time or another and the one we have now is AC only and on small inverter has been the easiest to use, most efficient for having better than TV speakers, and has been totally reliable over several years now.
If you do decide to use the built in speakers, I would ditch the multiposition switch and only input the surround sound amp outputs for speakers without the van radio option as with van radio on while driving all the speakers except the lowest range ones are in the back of the van. I would be able to give you a basic procedure for identifying all the wires after you take them off the rotary switch or find where it was. It is not a simple task but is better if you have two people.
