what case? MT, DT, SFF, USFF  , the case tells us what mobo is there, and are no the same. HW.

sure you can.

but UEFI is GPT drives only (setup ) not MBR.

can I presume the old disk ran MBR ok the cloned it MBR old to new 6TB MBR? this?

if yes boot the disk in CSM mode (compatibility mode) in bios , or legacy mode as some call it.

you really don't need UEFI do you, but do please say why first.? 

make sure the PC has no 3TB limits first (2.2TB?).  as many do, and IDK here.

2011 Q65 chipset maybe your only size limits(and then BIOS) if any..

also this cute clue, (wow)

only one SATA 6Gb/sec out of six,  put your SSD here ok?

boot to SSD and drive 2, the big drive, you wont be sorry.

on most old PCs this old, the UEFI code is only 1/2 baked (some are 1/2 done and the work ended) this is common

NOT saying yours is, I'd never claim ever to know anyone's undocumented BIOS, and nobody does, not really!

if UEFI is so important (unstated) then buy a 3020 for $50 and run that.  790s are like, cannon fodder. now.

790s go for $30 allday long at fleabay, fodder, to the masses. even $19 you pickup free.

IMO, I always look to see what better platforms are better at low cost, 3020s; wow.

 

790 is old, 

The MBR disk can be converted to GPT off line, (mean not booted to IT)

then in BIOS flip the UEFI bit (enable it)

 

UEFI mandates GPT formatted disk.

Legacy mode CSM can run both that and MBR , (many top brand PCs have CSM as a feature)

CSM outs UEFI shell around old BIOS. in many cases.

if you must have secure boot, then run UEFI, and GPT.

the real issue is rootkit malware. infections, and it is very easy to buy software that blocks this,

I run 3  layers of that.  but sure most folks will benefit from UEFI even if the DVD and USB stick does not  boot and you must turnoff  SECURE BOOT.