Question on home theater/music listening set up

Hey all! I am new to the forums. I was introduced by another member here and I have to say I am blown away by the amount of information on here. 

My question lies in the 7.1/7.2 surround sound systems. I will utilize my setup to watch movies, tv, and when I have the house to myself I love to put on some older 80's rock and sit and enjoy the setup. I love to dabble in classical music and for some strange reason I love horns. I am a big lord of the rings and game of thrones fan, and during battle scenes with drums, horns, ect I want to feel it in my soul haha. I love what I currently have, but I am trying to polish out what I have. I am open to suggestions on any brands that may go well with what I have now. My price point is primarily the used market. If you could just suggest the speakers you think would compliment the system I can attempt to find the best deal on those as possible. 

My current setup is as follows:

Polk Audio SDA-1A
Polk Audio SDA-2
Velodyne Minivee 8
Monitor Audio MR center channel

Denon AVR-3803

Power Conditioner-
Belkin AP41300-10

I have looked into ELAC, B&W, MIRAGE, PARADIGM, SVS, Ect trying to find something I like and I finally figured I should open it up to you amazing individuals to lend me a hand. 

Thank you in advance!
Have you looked into room treatment first? They make all speakers sound better. GIK Acoustics, Michael Green Audio are good places to start.
I havn't. I just started into the home audio scene. I am currently out of town on work and have been finding deals on the equipment stated above so that is what started the whole audio process. Currently I do not have a designated room to stage these in. I just know I am looking for a 7.2 setup and was looking for suggestions on another set of speakers that would add more depth to what I currently have.
ELAC is warm (the designer even states so), B&W is bright (good for low-level listening, though the employ a dip in the crossranhe which I hate), Mirage is meh, Paradigm is fine, SVS is fine.

The NHT C3 bookshelves or C4 towers, and whatever its matching center is, would sound awesome.

Also, a puny 8” subwoofer doesn’t even come close to good enough for movies. A Rythmik F12 would blow it away. If you decide to upgrade, play the first opening scene of Edge of Tomorrow on the 8” and then on the Rythmik (turn down volume to be safe), or play Blade Runner 2049 (in the beginning when he flys back to HQ for instance), etc.  
i used to have an 8”, thought I wouldn’t need to upgrade as it sounded good, but did upgrade and it was not even fair to compare (granted, my 8” was much cheaper than yours).
I’ve been wanting to get an additional sub. I figured I would use the 8” for tighter bass notes and get a 12 for the rumble. I’ll have to look into NHT. I am constantly being brought back to the thought of my ideal system being one in which I feel like I’m right there. Whether it’s a symphony or an action scene I want to be able to feel like I can reach out and touch the instruments. Obviously I’ll need higher end stereo equipment for this but I feel the polk set up has been giving me what I want; I just feel there is just something missing and I need to round out the 7.1/7.2 anyway so I figured I would look into branching out and getting another paid whether they are bookshelf or towers I’m open to both. Thank you both for your responses. I am open to anymore info, advice, critisms, ect I’m here to learn! 
100% fabricated myth that an 8” is tighter than an 18” (though it should be obvious that a $500 8” is likely better quality than a $500 18”). A well built subwoofer is good no matter the driver size. Rythmik’s owner has a Ph.D in Electrical Engineering, he knows what he is doing (not to put that on a pedestal, as HSU’s owner, Dr. Hsu, has a Ph.D in Mechanical Engineering I believe), and he has a whole list of web articles explaining how he gets good performance:

Rythmik, HSU, and PowerSoundAudio (co-founder of SVS) all make excellent bang for buck subwoofers; maybe a $2500 Vandy is better than a $1000 Rythmik/HSU/PSA, but it’s not better than a $2500 Rythmik/HSU/PSA.

Rythmik even takes a shot at Velodyne on their F18’s page:
The independent test lab site has published the max distortion numbers for F18 and Velodyne DD18+ (courtesy of Josh Ricci). The F18 has lower distortion and yet more output than Velodyne DD18+ for 1/3 of the price. In addition, the test results also include the impulse response of 18hz high damping which shows minimal ringing, a testament of F18 articulation bass sound.

I’m currently in school for electrical engineering and that’s my goal is to get into audio engineering. I’ll have to check out the brands you mentioned. I’m excited to have all of this good info and new brands to research 
I just added an Anthem 520 to my 5.1 and it’s a huge upgrade.  Their room correction software is great and it sounds so much more immersive.
Someone I know 😉 has a ATC 5.1 speaker package for sale on AGon and also has a great amp and processor that can be added for a reasonable price 😂. You can take it up to 11.2 and includes room correction.

just saying 

My 2cents FWIW, them old Polk SDAs are awesome for their age.  They will blow many away with their soundstage. That said, they really can be improved upon by a relatively low expense room treatment and optimization. Why do I say this? My HT system was set up around vintage Polk. SRS-SDA 3.1TL,  CS350LS,  FX500I. A subwoofer will really help here. After room treatment I was IN and part of the action on the screen. Used it for both HT and 2Ch and never regretted the cost of the treatment. Just sayin!
If I wasn’t in a rental house currently while finishing engineering school I would look into room treatments. My main goal was to just polish out what I had and then start hearing more toward room treatment and go from there. Wasn’t sure if I should try and add a pair of speakers with a more designate bright tone since the polks cover what I feel is a good warm tone. I’m looking at adding another sub for more depth and rumble. 
For what you're looking for and the music you listen to, a BIG +1 for ATC speakers.  Power and dynamics second to none IMHO. 
anyone heard the Polk audio sda-crs? wonder if i should round everything out with another set of SDA's
The sda-crs can sound superb in the right environment. For just about anything you want to know about Polks vintage sda-srs speakers go to the forum on Polks website. Great people on there and they know their Polks.
I myself love the vintage Polks, the mass production Polks not so much.
" Rythmik, HSU, and PowerSoundAudio (co-founder of SVS) all make excellent bang for buck subwoofers; maybe a $2500 Vandy is better than a $1000 Rythmik/HSU/PSA, but it’s not better than a $2500 Rythmik/HSU/PSA. "
Agreed and,Any of those.including SVS,would be super impactful right out of the gate.TWO Subs would be really the way to go.