I know you have built several speaker and subs and obviously like DIY. I am still writing this reply the way I am in case other folks think about DIY are following the convo.
Unless someone really wants the DIY experience (which I do highly recommend) the price point you are at is not offering much of a gain vs retail gear. You might not really save any money.
You would be doing it mainly for enjoyment.
@150-160 a pair, plus some additional costs, the Overnight sensations and C-notes are about as cheap as it gets for DIY.
I do think in the DIY realm, the C-notes are a very nice choice in terms of a nearly complete(box included) pair of speakers for $200. That said, note that a huge part of the C-Note speakers appeal is good bass for the size. Using a sub negates that a bit and definitely running them sealed negates a lot of the C-note design goal appeal. Especially as the design trades efficiency for bass extension.
I built the C-notes and have compared them to several retail speakers. They are okay. East to listen to with okay bass for a small speaker. Need plenty of power as they are really inefficient. Not a huge fan of the highs, they are kind of nasally and lacking detail. Whatever, they are fun enough and satisfying to build if building is satisfying for a peep.
Compared to a few quick retail examples I think the $280(pair) ELAC b5.2 is a better speaker. The $150(pair)Sony SSCS5 is better except bass wise. Without a doubt for my taste they get buried by the JBL 530 which is $240 in USA (what country are you in?)
Sale prices in the US can be crazy. My Sony's were $65 a pair. Just picked up a open box set of KEF q350 for $350. The C-notes do not compare very well to the excellent KEF speakers.
Someone mentioned the REVEL M16 which sound so much more like a hifi/high end speaker than the C-Note it is no comparison at all. Though they cost much more $, I am just trying to relate things here.
With sub bass help, I'd take the Polk XT15 over the C-Note and they are $200a pair - often on sale for $150 and even $99 in the US which is what I paid. With a touch of PEQ they are pretty great. If all 5 of your speakers are the same and require PEQ to correct the speaker you can, of course you won't be able to apply room resonance corrections equally, though you should still be able to get the sub eq'd.
I am not poo pooing DIY. Just putting some perspective. If a person has the time and it sounds fun go for it. I love doing it. I have built speakers I don't love though and they can't be returned and are hard to sell in the gear marketplace.
If a buyer goes up in price one may or may not realize meaningful gains for a small system. If someone was building a "bigger" set-up with really high fidelity aims DIY still poses issues, even though at higher prices some DIY gear is really great, because some is just okay. Plus there is personal preference which I feel is big factor especially when dropping a lot of time and money. Dropping hundreds and then hours or even more on a DIY speaker that you don't love isn't super fun for very many folks and at that point the fun part is reengineering them or repurposing the parts which makes this whole DIY thing into a real hobby( or for the unenthused, a time suck.)
I always say that if the point is to also DIY for fun and adventure then go for it, if it is to save money or to get the best you can for low $$ it may be safer to buy retail on sale or clearance or even full budget prices in some cases are competitive with entry level DIY kits.
anyway,
You do personally like DIY and you live in country where the JBL 530 likely isn't on sale for $240 a pair or similar deals are not to be found. I also realize the point is a very affordable 5.1 system. Hifi/high end sound is not the goal, so cloning the Performa3 line would be to expensive vs the goal. I think to bring it back around for a modest and highly enjoyable HT your original choices of are still the best options currently.
Other options that you (or other DIY interested folks)may not have seen yet if spending a bit more.
$250 pair Zaph ZA5.2
https://www.madisoundspeakerstore.com/2-way-speaker-kits/zaph|audio-za5.2-tm-2-way-pair/
$282 no boxes/495 with boxes pair SB Micro
https://www.madisoundspeakerstore.com/2-way-speaker-kits/sb-acoustics-micro-2-way-speaker-kit-pair/
$480 pair no box SB Bromo
https://www.madisoundspeakerstore.com/2-way-speaker-kits/sb-acoustics-micro-2-way-speaker-kit-pair/
$125 each w baffle/no box S2000 MTM
https://www.diysoundgroup.com/home-...-series/s2000-speaker-kits/s2000-mtm-kit.html
If the Hivi kits are available in your country maybe check into those.
The old PE design still seem like decent ones.
$100 each for the Classix II kit at PE is another option, they have great bass response according to others(I have never heard them)
https://www.parts-express.com/Classix-II-MT-Bookshelf-Speaker-Kit-with-Baffle-Only-300-7110
$200 a pair for the BR-1's, these are a sealed box design with good bass
https://www.parts-express.com/BR-1-Kit-Components-300-641
Hopefully you can figure something out.