not ideal but u should front height is sometime better than elevation (reflective) one.

a lot of HT users live with compromise. just do what your room and gear allows.

yes.

you can go to manual setup > levels > run test tone , using SPL meter with weight C, Slow  to check each channel speaker include Sub-woofer 75db . But be careful, some SPL meter is not be calibrated properly, may got +- 1.5db error. My SPL meter got this issue, after I compare with my friend SPL meter, find out my meter got +1.5db error.  So i always adjust my speaker to 73.5db, but the sound setting is correct.

your situation, Better leave default level after calibration. Do not use Phone app, too much error.  Normally  Audyssey auto level quit accurate, If you measure multi point  mic  position.  Even got error, only 0.5db error.

do average using phone.. if ur phone manage to match 3 or 4 speakers with the same db says 73db then u just make sure other matches 73db..

no need to match 75db.. if your audyssey work well and you did your placement correctly.. most speaker should fall around the same db.. only 1 or two speakers need to be adjusted.. thats all you need to do.. no need purposely reduce to 75db.

One note about Audyssey calibration - if you don't place the mic right, the variance between each seat during multi calibration can vary significantly. So I hope you weren't using the dumb card board stand Denon includes with the receiver, but instead using a boom mic stand to hold the mic.

this type better.. less reflection.. even tripod itself will reflect sound to the mic

yup.. life is not perfect isnt it?

I think you have your priorities wrong.

You should change your front LCR first before anything else if you're intending to change your entire sound system setup. I'm using SVS elevations, they are good height speakers but to be very frank they don't add very much to the experience. In fact I think they're overpriced and on hindsight I'd rather use cheaper in-ceiling speakers instead. Point is, changing your height speakers won't make you notice much of a difference (if any at all) to your overall soundstage.

Unlike height speakers, changing the LCR can amount up to a day and night difference. So place your budget here first is my advice.

As for the sub, there is no contest between a the Polk HTS 10 and a similar sized SVS 10" sub which SVS does not have. The closest is the SB1000 Pro and that blows the Polk HTS10 out of the water, not even a fair fight.

My opinion is that the most optimum way of upgrading is (assuming you continue to use your current set of speakers):
Subs (yes multiple) > minidsp 2x4HD > LCR > then whatever you want after that.

Don't just upgrade because your heart tells you to, upgrade using logic and common sense. You save and learn more at the end of the day.

I agreed with SSJBen that if you r planning to upgrade LCR you should focus on that first.. that is where most of the sound come from.. others are just addition.. you got a nice ceiling or reflection speaker which do maybe 10% to 30% of the movies playback but you are not happy with your primary which do 80% of the job.. you want to reconsider bro..

yup get your subwoofer too if you havent got it.. surround and ceiling can come later..

just keep on doing research, save the money, and buy the LCR that you wanted. preferably all LCR be the same speakers. once done, buy the same speaker for surround use.

for the subwoofer, you get what you pay. big driver with reliable power amp not cheap.

u need to do lots of measurement and fine tune. if possible, don't. the 8" will end up distorting badly.
not just same brand but same model 

How big is your room? That is a key component to know on what sub size to get.

You can match different sized subs yes, but you will need measurement tools to gain match and time align them properly. So a calibrated measurement mic (UMIK-1 for example) is mandatory. You will also need quite a bit of time to do this, not a 10 minutes job.

You have to account for the entire space, whatever your living room is open up to (dining area for example). Bass lengths are very long, so you can't just calculate based on the area where the sub is at. 22x10 is on the average side, you may want ported subs instead (PB1000 Pro).

Will recommend ported subs then for sure.

Depends on your budget though, a pair of PB3000 will be very nice for that space and if you don't mind disturbing the neighbors. But if you can't stomach that budget, even a pair of PB1000 Pros or used PB2000s is a good choice.

ok.. now we have another happy owner.. another 2 annoyed neighbours 

U bought from the right guy.. most of the time he is very helpful 🙂

When they back and knock your door, you just tell them
"we can't go cinema for so long due to covid-19, so I brought the cinema back home"