It is not an Axe-Fx. It won't be able to do two amps or two cabs. It won't have things like the Vocoder and other esoteric blocks. It's a stripped down floor version at an aggressive price.

It will have G3 modeling and user IR slots. It has two dual-core DSPs, one for amp modeling the other for effects. These DSPs are slower than the ones in the Axe-Fx so it won't be able to do two instance of amps.

There will be block compatibility between the Axe-Fx and the AX-8 meaning you can copy blocks from your Axe-Fx presets into the AX-8.

It has USB, XLR outs for FOH, 1/4 outputs for local monitoring and an FX loop. Four expression pedal inputs. AC powered, no wall-wart.

A DSP unit dedicated to performing a defined task. In this case it performs convolution. The difference is that a "DSP" as we commonly call them is really just a microcomputer optimized for Digital Signal Processing. The term DSP most correctly refers to any device that does signal processing using numerical computations. That device can be an FPGA, ASIC or fixed hardware unit. In the AX-8 it is a convolution processor.