Upgrading to replace A10-6800K with new AM3 mobo/processor

Just so you know, AM3(+) is an older socket. The FX CPUs were released a year before your current CPU. You'll have more cores, but those cores will individually be slower than the ones you already have. I recommend strongly against "upgrading" to a CPU released in 2012, in 2017.

am3 is dead, fm2 is newer


wait for ryzen or get an intel setup

There really is no upgrade from your CPU that is meaningful from AMD today

This would be a good mid-priced combo:

PCPartPicker part list / Price breakdown by merchant

CPU: Intel Core i5-7500 3.4GHz Quad-Core Processor ($198.88 @ OutletPC)
Motherboard: Gigabyte GA-B250M-DS3H Micro ATX LGA1151 Motherboard ($73.98 @ Newegg)
Total: $272.86
Prices include shipping, taxes, and discounts when available
Generated by PCPartPicker 2017-01-26 18:59 EST-0500

Pair it with 2x 4GB or 2x 8GB of DDR4 2133 or 2400 and you're good to go.

EDIT: You mention wanting to get away from mATX. What in particular are you looking to get away from in it?

Hey Dan. What's your price point? There are a few options. I can't blame you if you don't wait for AMD Ryzen since I upgraded from my FX 8320 to an i5 6400 literally last week. If you can wait, I would. If you're impatient like me, you've got options now. As it's been stated, AMD has nothing to offer you now. I've had the unfortunate experience of wasting my money on AMD* but because of that I can shed some light here.

*I build my computer in 2012 with a $1000 CAD budget. This left me with an Fx 4300, GTX 660, 1TB Seagate Barracuda (don't do it), and 2x4gb of GSkill ram, and the rest of the build. I "upgraded" (mimicking the above pov) my FX 4300 to an FX 8320. I had no idea how wrong of a decision that was until I noticed almost no improvement to gaming. The FX 8000 series has it's place for productivity, but for gaming it makes absolutely no sense. A lot of people recommend the FX 6300 for a budget build, but even that is misguided. Without continuing this tangent, just know I have gone down the AM3+ path and learned my lesson.

If you don't want to wait for Ryzen, I would recommend you moving to Skylake. You can do what I did and grab an i5 6400 and Z170 motherboard that will let you overclock it (BIOS flash required, very simple). http://overclocking.guide/category/intel-oc-guides/skylake-non-k-oc/ Check through these for a motherboard you'd like. I settled on the Gigabyte Z170x Gaming 3. It has everything I need, including proper heatsinks for the CPU MOSFETs. It doesn't break the bank either.

This method of overclocking is very simple, only effects your CPU and Ram, as opposed to PCIe and sata, etc. This means your computer will stay stable at high BCLK overclock levels. Also, this only works for SKYLAKE CPUs; turning any non-k CPU into an overclocking monster. My i5 6400 is currently at 3.9Ghz (stock 2.7Ghz) and if I spent more than 10 minutes in the BIOS I'm sure I could get that higher; aiming for 4.5Ghz.
The same can be done with i3s if your budget doesn't allow for an i5.

I would highly recommend getting an i5 so you have four cores (w/o hyperthreading) as opposed to an i3 with 2 cores (w/ hyperthreading). Either way, you will see large performance gains in pretty much every game, day to day use, and productivity. You're in a great position to upgrade to Skylake and will notice huge improvements for your cash. I would highly-highly recommend getting a z170 mobo, non-k cpu, and overclocking it like hell. You will have to spend a few extra bucks on a cooler (Cryorig or Cooler Master have very good options for cheap prices).

Let us know if you have a budget and a list of components you will need (remember, upgrading a cpu means new mobo, ram and OS as well).

Best of luck!