adding center speaker to existing stereo system

good point erik.

"I think the idea that you should ONLY add a matched center is unnecessarily puritanical, and my own listening tests have shown to me that adding a different center, when done right, is a big improvement over a phantom center. Have you done this experiment?"

Sorry Erik, but again I must respectfully disagree, and yes, have done the experiment. When evaluating a client’s existing system, I would have them compare the way it was to using phantom center. Never had anyone with a mismatched center to say it sounded better and some with timbre matched even like phantom better. Dialogue could be adjusted louder with a mismatched center but the entire front image and overall sound was worse compared to using phantom. This definitely prompted many to upgrade and get as close as possible to 3 identical speakers on the front.

And yes, I have experience with room correction and DSP. It can help a little, however it is not a magic bullet and can not make a mismatched center have the same tonal character of the L & R. If it was that magic bullet, you could take 2 different speakers and make it sound like a stereo pair. I don’t think so.

Yes, the center speaker plays dialogue, however it affects the entire front image and sometimes that dialogue can be produced by the center and a L or R speaker depending on where that person is located in the picture. With a stereo pair, a single front image is created, but when a center speaker is inserted, that entire front image becomes much more complex. 3 identical speakers and that works easily with tonal character remaining consistent across the front. A mismatched center can provide louder dialogue, but at the expense of severely degrading the front image and tonal character within the image. I have heard many systems in which a vehicle moving across the picture sounds normal on each side, but much smaller or different at the center position. Now if the OP needs a center for off axis listening, that’s a different issue. I did reference that in my first post, however he has not responded.

Sound bar? Surely you can’t mean to use it with his current system. What a mess that would be. Assuming not, and using it alone compared to his current system, and I’ve got to assume this added TV is between the L & R speakers, no brainier, I’ll take the system.

Again, I must stay with my original recommendation that if he does anything, it should be rear speakers to get room filling effects and forget the center unless there is an off axis listening issue.

So Erik, sorry to say that it looks like the only thing we will agree on is the fact that we disagree, and that's ok, as everyone is certainly entitled to their opinions. Also, keep in mind that I speak from experience with many clients and it’s not just "my" experience.

@auxinput, why not a pair of rca to xlr cable with xlr passive preamp or switcher for Option #1?

Just picked up on this thread.  I'm was a Jim Bongiorno fan before his passing.  He tackled this deeper than anyone else that I've seen.  This is a terrific item, take a look. 
https://www.sst.audio/new-products/trinaural-processor

@imhififan - I suppose you could use a RCA to XLR cable, but it's really not the right way to do it. On this RCA to XLR cables, the negative polarity signal wire on the XLR is connected to the shield/ground on the RCA.  You really should have a Jensen transformer converter box here to convert the RCA single ended to a true balanced signal if you want to do it correctly.