1) What dimensions does it have AFTER you take off the stands?
2) What weight does it have after you take off the GPU and the power supply?
You want to carry that into the cabin without the box?
AFAIK, not possible. Normal carry on baggage size limit is 56x36x23 cm, and the 7,1's dimensions is ~53x45x22 cm. That 45cm exceed by too much. No way to do that officially (remove the stand won't help)
Of course, some check in counter / airport staffs don't really care. And as long as you can get that onboard, most likely no body will ask you anything (it should be OK to fit that into the overhead compartment. I often put over size bags into there. The 7,1 will be fine).
Weight of course will be over the limit by a lot (18kg vs 7kg) as well, but if you remove all PSU / GPU etc, may be it can be very close to 10kg. And as long as "it doesn't
looks too heavy" when you are carrying that (e.g. in a large backpack), usually no body will try to measure its weight.
However, there is really no guarantee that you can do it. As long as one staff (e.g. a cabin crew) try to check its dimension / weight. You will have no choice but put that into the cargo hold. It will be very bad if you are already onboard, and no box to pack the 7,1 properly.
IMO, it will be so much easier to put the whole box into a large check-in baggage. Just fill the box with lots of clothes (or even foam) to further protect that box. Then it should be fine.
The 7,1 was shipped inside that box from the factory anyway. It should have enough protection. Of course, when they were coming out from the factory, they were in a large group. And lots of boxes were tided together as one large piece of freight, then loaded by the machines (individual loader cannot "throw" them). However, still won't change the fact that the partition inside the box must be strong enough to handle some very bad turbulence (or sudden drop, etc).
So, IMO, as long as you have a big bag that can contain the 7,1's box with lots of sock absorber, that should be fine. Much safer and easier than no protection but put it on an overhead compartment.
If you want to be safer, just tell the airline that you have valuable and fragile items inside your luggage, and tell them the correct orientation of the luggage (do not ship it with any other orientation). The check in counter staff should able to put the correct sticker onto it, and let the loader to handle it correctly.
In this case, most likely the 7,1 can survive.
