Greetings,
 
                  I recently took the plunge and ordered the Hybrid kit for my 3080 Ti. My concern is where would be the best placement for the radiator of the hybrid? I currently have a Lian Li 360 AIO placed on top as exhaust, 3 120mm fans as intake in front and on the side, and 1 120mm as exhaust at the rear. I was thinking of placing the CPU 360 AIO on the side as intake and the hybrid at the top as exhaust? Any constructive opinions are greatly appreciated?
5000D AIRFLOW Tempered Glass Mid-Tower ATX PC Case — White (corsair.com)

If you have to run one as intake the GPU might benifit more from the cooler air. This might get you down into a lower bin. The 5000D looks like you could do top and side exhuast to avoid exhausting either of the aio's hot air into the case. 

I had 2 360 AIOs , I did GPU on roof and cpu on side exhausting and 3 fan intake , I like the GPU on the top because I think the Asetek pump is not as powerful as the EK cpu AIO.

B0baganoosh
Personally, if it fits that way, I'd probably set up the AIO as a side exhaust, the GPU rad as top exhaust and front as fresh air intake. I have had bad luck having hot rads intaking air as then you have a case full of hot air...I think your CPU rad would work fine either way, but the GPU rad on intake will cook everything else in the chassis. I did that when I first put the hybrid kit on my 3080ti (had GPU intake and CPU exhaust). My GPU temps were fine, but my CPU started cooking. Now I have fresh air intakes and both rads exhausting and it is working much better.

If you go this route, just be aware that you'll need to adjust fan speed if you want positive pressure, since using both rads as exhaust will mean you'll have more fans blowing out than in.

Incidentally, I have a 3080 Ti in a Corsair 5000d airflow case with a 360mm aio rad for my cpu.  After experimenting with various setups, I put my gpu rad as exhaust out the top and the cpu rad as intake from the front.  I also have three fans intaking from the side and one exhaust out the rear.  This seemed to work best for me.  I tried putting the cpu rad as intake in the side, but I think it gets better airflow and stays quieter when mounted at the front due to that case generally having better airflow in front than in the side, and also due to the configuration of the air filters.
 
Edit: I also have a fan kind of laying on top of my gpu blowing air downwards.  This doesn't really have anything to do with gpu temps but rather to make sure that an NVMe drive that's mounted behind the gpu has air flowing around it since it was running on the warm side and was kind of blocked off by the gpu and wasn't getting good airflow as a result.

Ciddharthas

B0baganoosh
[snip]

If you go this route, just be aware that you'll need to adjust fan speed if you want positive pressure, since using both rads as exhaust will mean you'll have more fans blowing out than in.

Incidentally, I have a 3080 Ti in a Corsair 5000d airflow case with a 360mm aio rad for my cpu.  After experimenting with various setups, I put my gpu rad as exhaust out the top and the cpu rad as intake from the front.  I also have three fans intaking from the side and one exhaust out the rear.  This seemed to work best for me.  I tried putting the cpu rad as intake in the side, but I think it gets better airflow and stays quieter when mounted at the front due to that case generally having better airflow in front than in the side, and also due to the configuration of the air filters.
 
Edit: I also have a fan kind of laying on top of my gpu blowing air downwards.  This doesn't really have anything to do with gpu temps but rather to make sure that an NVMe drive that's mounted behind the gpu has air flowing around it since it was running on the warm side and was kind of blocked off by the gpu and wasn't getting good airflow as a result.

True. I have some pretty high-pressure fans as intakes with my "all rads exhaust" setup (the rad fans are high pressure fans too lol). The airflow pushed by each fan is reduced greatly when the fans are pushing through a radiator. So you can usually have less fans intaking (without radiators) create more pressure than the exhaust fans that are pushing air through radiators. In my case, one of my intake fans is a Noctua NF-A14 industrialPPC-3000 PWM, which can push 6.58mmH2O, but it sounds like a vacuum cleaner to do so, so I generally only have it push up to about 60%-max. Even there...it moves a LOT of air. I think it's overkill for most people, but my case was not optimized for airflow and I had to run some of it backwards and with limited fans, so desperate times called for desperate measures. With the 5000D, I think 3 intake fans on the front would be sufficient, especially if they turned them up a bit higher than the radiator fans. The rear exhaust fan could either be rotated to be additional intake blowing on the VRMS (and feeding the GPU rad) or could just be kept at a nice and quiet low speed forever lol.
 
Generally, the CPU rad is going to be moving much cooler air than the GPU radiator, so your approach is also great! I definitely wouldn't argue against it, especially because you've tested in that case. The one time I wouldn't want that is in games like Battlefield 5. I'm not sure how many have similar situations, but when loading the next map in between rounds in that game, your GPU is already warmed up (and still rendering content) and then your CPU pegs to 100% for a minute or so while loading the next map. So it can get toasty if you have one radiator feeding the other. That said, I don't think a little extra CPU heat is going to hurt the GPU there. I think worst case scenario it just gets a little warm for a few minutes then cools back down over time. Benchmarks generally only hit CPU or GPU, but not both simultaneously, so it really shouldn't be an issue in most use-cases.

You guys are awesome. Thank you for the feedback. I think I will go with what Ciddharthas has suggested and maybe turn the rear fan around as B0baganoosh suggested as well.