Hello,
 
I have not had any customers comment on issues with PSU cable lengths in their DG-8 chassis so I think you'll be okay.

Ok 

09973
I did 30CM extensions, via tape measure that seemed logical for my wires especially my 24pin ATX cord for my superNOVA 1000 T2 PSU..... stock cable does not even come close to reaching which is now routed in front on the motherboard until IceModz decides to ship my cables :/ Lucky the PCIe cords were long enough.... just. I just never commented on the cable lengths before since I kind have expected the lengths to be a bit of an issue. I had plans to remedy with extensions as I bought the case if needed.
Results may vary and I do not even know if I am correct. 

Ok thank you having pure custom cables put in and my psu is the same to be honest couldn't do the cable management since it was too tight to do it 

I can comment to this, as I have done both stock length (600mm) and extended (750mm) cables... Realistically the only cables you are going to have to be concerned with on the PSU is the 24pin ATX. Some PSU's have the 24pin leads plug into the left of the PSU (side closest to the plexi door) which causes some just barely making it scenarios, depending on the PSU. I personally have a Corsair AX1200i, the stock setup for this has a 600mm ATX cable, and the leads for it goes into the right hand side of the PSU (toward the back panel of the case where all the cable management happens) - since this one is on the right, it frees up about an inch, maybe 2 inches of length when getting it all hooked up. I wanted to have extra cable for the 24pin so I could route it better, so I spent the money for a custom 750mm ATX cable, and was able to route it perfectly.
 
Example of PSU 24pin locations:

MB/24pin/ATX located on the "left" which would reduce the length you have to get to the 24pin on motherboard, this causes it to be a sort of strained connection as reported by some reviewers and owners...

 
Example of MB/24pin/ATX located on the right hand side, which gives a little extra slack when dealing with the 600mm stock cables:

 
The only other things to be concerned with, but depends on what you are doing is the SATA power cables, and if they can reach all of your drives in the stock mounting locations, usually the locations on the back will give you the most trouble - the other is the SATA cables themselves, you will want 50-60CM cables if youre running from the farthest 3.5" and 2.5" mounting locations, and opt for the 60CM if you want a bit better cable management.
 
This is what the back of my case looks like with everything done.