TV/home theater/surround sound (my old stuff, but, example for tv/music solution):
Watching TV, you want a 'wide center', many music speakers are for a precise center, off center loses one channel, and loses center, loses imaging.
I got these DBX speakers for my home theater fronts, they are specifically designed for a wide center, I love and highly recommend them.
http://www.hifi-classic.net/review/dbx-soundfield-100-135.html
Left speaker aimed a bit more to the right. Right speaker aimed a bit to the left. When you sit off center, you are now closer to the left speaker, however, the right speaker is aimed at you, maintaining balanced left/right/center image.
3 tweeters each, maintains high frequencies hither and thither, front facing primary tweeters for imaging.
Surround Sound
Because Dolby separates the center/dialog information, your front left/right speakers don't get that information, thus cannot create a center image, soooo, even though your main fronts are magnificent, you need a dedicated center speaker. The center channel speaker location wants to be as close to the bottom of the TV as possible, to keep the sound origin best. This Bose Center Channel is small but terrific, and blends very nicely with the DBX.
https://www.ebay.com/i/323988054675?chn=ps&norover=1&mkevt=1&mkrid=711-117182-37290-0&mkcid=2&itemid=323988054675&targetid=475515050541&device=c&mktype=pla&googleloc=9003512&poi=&campaignid=6469981122&mkgroupid=79220336802&rlsatarget=pla-475515050541&abcId=1141176&merchantid=115052798&gclid=CjwKCAiA9JbwBRAAEiwAnWa4Q0WuGZpjh1Knb79c8IRIyPLOkHgFvBx3a0b04uo0DSJxiOyFpT_XMxoCydwQAvD_BwE
Use your receivers volume settings to balance the volume, the frequency dispersion of this Bose melds well with the DBX. Remember, Bass will not be sent to the center, so small good centers can do a great job.
Rear, you know how to solve that, just a comment, many people set their rear speakers too loud. Best is if you are generally unaware of them until you turn them off and the image collapses to the front. Specifics, heliocopters from the rear, you will definitely be aware of.
1 Subwoofer or 2 Subwoofers: Definitely different needs TV/Music
One sub can be very successful in home theater, however, two subs can be better for music.
Dolby 5.1 will take the low bass away from the main fronts, so, fronts don't need to be as full frequency as for music only. However, when using 2 channel stereo mode, the bass of your fronts should be good on their own.
Music subs. I recommend a stereo pair of subs, directional, bass is not mono as many like to believe.
Music
IF a 2 channel source, or, a phony surround created from a 2 channel source:
You want to Turn all surround effects off, set your AV receiver to 2 channel only. Now you have a Stereo Pair, still with a wide center. All sound will be coming from front l and r only, sooo the amount of bass will be determined by those mains. The DBX have enough bass for music without a sub, I added the sub for Jurassic Park dinosaur stomp, that sort of thing, but is gets no signal 2 Channel mode.
Direct. Watching music programs, like the Voice, the receiver will sometimes automatically select some surround, you can change the receiver to Direct. Now, if surround is being broadcast it will keep that, if the original is 2 channel it will use that.
It is quite obvious, and the music can be much better using 2 channel mode.