Final Setup Update!

If this is for gaming, you are overspending on many items. RAM, 16gb is plenty. 1200w PSU? What for? Get a quality 700-800w PSU and call it a day. CPU if you arent going to OC, motherboard if you arent going to OC. Might be helpful if you said what it is for. If its just for gaming, yikes.

What is your overall budget for this setup, including everything mentioned above???

The Maximus IX Hero is not very good value for money. I would suggest any of the other 2, specially E Gaming. Its good value for money and comes with wifi and Bluetooth... https://us.hardware.info/comparisontable/products/377817-373875-379613

Is this a build or a list of the highest priced items?

The RAM should have no issue as I recall. Go to Noctua's website and check the specs on the d 15, which are there in detail, and then do the same for the ballistix sport ram. Some suggestions. Screw the coolermaster psu, you could find one for around the same price or a little more that has better overall efficiency and functionality, e.g. one of the latest Seasonic, Evga (superflower oem), Corsair gold or platinum lines. You don't need 1200w for that sli build, lower the wattage to 850 or 1000 and get yourself a quality psu instead.

Mousepad... For far less than $30 you could get a far better quality pad, e.g. from redragon, reflex lab, glorious, many more. They're far better quality for your money, come in varying sizes and thicknesses, are durable, washable, imho far superior than the expensive brand named ones. SSD: Why settle for a 850 evo 1tb when you could get a 960 M.2 evo 512Gb (more than enough space for most), pro, or even a MyDigitalSSD BPX for the more budget conscious? The M2 960 evo & pro far surpass what you'd get with a 1TB 850 Evo, and use an inexpensive 7200 speed 1TB or higher HDD for programs or files not currently used, or used as much .

Last suggestion. You can build your own headset. Start with a decent pair of headphones and slap a vmoda mic onto it, and choose an inexpensive 7.1 surround sound adapter if that's a thing for you, though tbh you'd be better off dropping the 7.1 SS, it's not true surround sound on phones anyhow. You'd get better value & sound quality if you make a decent choice, and for a tad more (or considerably less even) than the $239 you'd end up spending on that overpriced senn headset. For around $239 you could get a decent pair of phones, eg Phillips X2, or beyerdynamic dt770s for half that price, etc. Don't get me wrong, far as gaming headsets go, the one you chose is one of the better/best. Gamezero is more comfortable overall. If 3d sound in a headphone is your thing you could look into a less expensive pair of Ultrasone HFI-780 S-Logic Surround Sounds, or even a pair of used or new 900's if u find a sale. If you have a decent source powerful enough to drive them, you could even get a pair of Foxtex T50 RP Mk2s or Mk3s, of one of their beautiful modded variants (mad dogs, argons, talos, etc) can't do much better for planar magnetic phones for the price, imho.

you could get 100% the same performance for 90% of the cost, and 95% of the performance for maybe 70% of the cost.

Not a very optimized build. You are spending too much extra.
As for the initial question, Obsidian is a Full tower and should house the Noctua ideally. The combination of D15 and 750D doesnt show any incompatibility in PCPP either. But the Noctua unit you have chosen is probably the largest available around. So the RAM has to be low profile to accommodate the same.

Do you really need to swear? Enjoy overspending for epeen!

If that's really the case, then why bother with any subpar components at all? Go for a Seasonic Prime PSU, or if they haven't built one at your desired wattage, try Evga or Corsair platinum lines that go up to more wattage than anyone could need.

For headphones, get the Hifiman flagship along with an excellent amp and dac. Are you going to be OCing? Then do away with that D 15 and get yourself a custom loop that you could run your cpu, motherboard, and GPU's through. Heck, you want suggestions on how to spend more money on a better system? I and many others could go on all day. A 27" monitor with TN Panels??? Why not splurge and get a couple 4k IPS gsync monitors? The mousepads I told you about still stand regardless of money. You want the best mousepads money can buy? Look to Artisan, hand(?) made in Japan.

SSD?? How about a 1 TB M.2 960 pro or two in raid zero (lol) instead of screwing around with an 850 evo? I see you've already chosen a pricey mobo, but here's the sad thing about z270 boards. None of them can do SLI above 2x8 far as I know. Is that adequate? Probably, for now. Possibly see if any of them use a plx chip to increase available lanes, though I doubt it. You could always scrap kaby lake altogether and possibly consider an x99 board e.g. the Asus E/WS USB 3.1, more than enough lanes to do anything you want thanks to its couple of plx chips. Asrock also offers a similar board.

I get it, money is no object for your build. So why choose ballistix ram? Choose low profile ram with the best timings available, maybe something from Kingston or Corsair. Why an air cooler, or founders edition 1080 ti?? Wait until the better aib versions come out and consider a couple of those instead. Money no object and your going with a Corsair case?? Screw Corsair, get something you'll appreciate from Case Labs instead, something that you can customize to your exact needs and looks outstanding and made out of aluminum as well.

Keyboard: Meh... good enough, though something from Topre may suit a no budget build better =). Mouse... Get something you know you like, regardless of price. Find out what the best weight is for you and get it, Zowie is ok but there are tons of mice you can choose from. Shall I go on? You get the idea, all the same. If you can afford a $10k build then do it right. Dont neglect sound or anything else and for heavens sake don't get founders edition 1080 ti's.

yh if money aint a problem get the setup above and when you purchase it make sure you take a pic and show us so we know you actually bought it....