Area-51 AAT2250, forced to get a new motherboard, would an E-atx fit?

You'll face many challenges doing this -- essentially you'd be better off using a standard case and power supply, and end up with no warranty.

Assuming you're beyond the 30 day return period, you'd be better off selling the system for what you can get and then building a new system that's more suitable for your needs.

Any pre-built has some potential compromises but I think the A51 is one of the best out there now.

This is well known in the industry.

Also, just as with everything, sometimes you could get a lemon and that's too bad.

Build your own if you want max performance in a PC.

I doubt most users would even notice the difference though (with equal part selection).

@Element115s4​ thank you for your reply but I just need to know if I can fit an e-atx into this case, selling it and/or returning it isn't an option, besides, the case is OK, it's not the problem, the motherboard is, dell's restrictions are (the inability to use my own, third-party, faster better ram drives me nuts).

I already have a 1600w titanium psu, the conversion kit, all I need is to decide whether I'm getting a Z890 Asus rog Hero/Apex or if I can go with the best, aka ROG Maximus Extreme. 

Seriously, nobody knows whether or not I can fit an e-atx ROG Maximus Extreme into this 80l case? 

@ejn63​ I already mentioned the fact that it's not an option. All I need to know if whether I must use  a standard ATX ROG Maximus Apex or  if I CAN use an e-atx ROG Maximus Extreme, even if I need to make a few adjustments. Still, it will allow me to future-proof the system and not worry about being held back by Alienware anymore. Speaking of warranty: their tech support is such garbage that I don't need their warranty, they are, by far, the worst company I ever dealt with. First, after FINALLY getting to them, they forced me to reset bios, then re-update bios and then, when their attempts failed, forced me to reinstall windows. When none of it worked they attempted to do it remotely and destroyed the recovery partition by accident, which I fixed. All that to tell me that the 6400 mts/s CL32 ram won't work on my machine and that the ssd drive that magically died inside it, after being used only once, was probably faulty. They 'escalated' my request to Narnia, I'm guessing? Because, even though they said they did, the request can't be found and, despite the fact that I still have $450 worth of now-useless 64gb cl32 6800 mt/s ram the rig won't even boot with it installed and thus I must use the slow, <Profanity is never allowed. DELL-Admin> 32gb they supplied me with. I have never been more disappointed by tech support or by a company and its arbitrary, idiotic bios restrictions. 

You won't be able to drop in a standard mainboard -- plan on replacing the case with the power supply unless you're in for an engineering adventure.  Also budget for a new Windows license, as the OEM license cannot be transferred to a non-Dell mainboard.

I would recuperate as many items from the Dell system as possible and invest in a case that supports E-ATX boards, and move the components over into the new case.

You could also save some money going with a cheaper motherboard, which would give you the new case for free basically and then.

Honestly don't see the benefit of going with a +$1K motherboard, unless you plan on heavily overclocking and use nothing but the best components. If you plan on sticking with the Dell components minus the motherboard, a $300 motherboard will work just fine.

@DevilOnYourBack​ 

A third party mainboard to me is not really an option here unless you just build your own and scavenging what parts you can from the Dell.

I am making the argument that the Dell Mainboard is a big reason why I go with Dell.

Yes, there are some compromises in squeezing out every last ounce of performance. 

While I can understand you want that max memory speed for example but are you really going to notice in everyday use?

I bet not.

It's your money so do what you want but the A51 is an excellent Pre-Built and I have been building PC for decades.

@Chino de Oro​ thanks, much appreciated. They already sent me the conversion kit. They're the only ones who sell such an expensive machine without any ability to use third party ram and also having insane voltage limiters and such that prevent overclocking and won't allow me to use the system to its ability. I'm going with Asus Z890 Maximus Apex and a dark Power 13 1600w psu because I'm planning on adding another 120mm aio for ram/ssd cooling. 

Thank you again for confirming.