I utilize a GD09B for my HTPC case inside the entertainment center enclosure. I am not sure on the specific size differences between the two but will give you some of my own insights to the case.
The '09' is also an ATX sized case. From what I can tell it appears the major differences are the additional venting the 09 has as compared to the 08 and front panel material. The 09 is plastic rather than metal. It has room for a regular ATX power supply, (3) 120mm fans on the sides, and (2) 80mm fans in the rear. The way the case is designed has there being a drive cage for the external optical (CD) drive as well as a cage for a 3.5" drive. With that part in place there is no room for any cooler aside from possibly stock or otherwise "pancake" style coolers. There is an option to remove that drive cage which you can then use the 3.5" cage to mount it on its side towards the front of the case. This left room for one of the Noctua 92mm tower fans to be installed.
There is placement for 2.5" drive in front of the power supply placement. I have found that if you utilize a M-ATX motherboard that it leaves a small amount of space for unused cabling to go. With a full ATX board there will essentially be no room for cables aside from on top of the 2.5" drive. It is important to note here that you must hook up the drive power and SATA cable before mounting the power supply due to space constrictions.
If you remove the CD drive cage and also the brace that runs from front to back to make the case more rigid, there is room to mount a graphics card. A 3070 fit inside mine with no issue at all. The 1080 that I used there previously required 180* power connection adapters.
I am currently using the case with (2) 120 mm fans and (2) 80 mm fans. Due to wire length and the fan header placement on the mobo I used I optioned a fan hub mounted on top of the 3.5" drive for all the fan wires to reach back to. In my own case I am using a modular power supply to eliminate wire clutter outside of what is absolutely required. The cabling will be bundled over the 2.5" drive as mentioned above and also will block air flow from that fan location. It is also important to note the length of the graphics card. The 24 pin and CPU power wires are most likely going to be routed "in front" of the GPU along the front side of the case. If you have a really long graphics card it can make running those a bit more difficult for space. There are several spots alongside the front panel and well as along the bottom tray for places to utilize zip ties for wire management.
My own system is built out with an 11600K on the cheapest M-ATX motherboard I could find, the aforementioned NHU9S cooler, a reference 3070, and Corsair RM750X. I have the OS on M.2, a 2.5" drive for game storage, and a big HDD for movies and backup type data.
The biggest detractor that I can think of is the placement in relation to my own system. Since it is inside an entertainment center and enclosed on all sides but the front it lends to getting quite warm while gaming. For media consumption and web browsing it doesn't present an issue. When gaming the system gets quite warm and as a result, quite loud as well. I have found that placing a small fan out in front of the system blowing into one side of the shelf it is on mitigates this issue. You mention your own system being mounted under a desk so you likely will not have the issue where it remains trapped in with its own heat.
Anyway, I hope this helps a bit for some insight into using a case like this. Good luck with your build.