Great news,
You bought a mixer that is perfect ( I mean PERFECT) for your recorder (and vice versa). A8 being 4 input doesn't complicate anything because the m1508 is also only 4 bus.
I have an m1508 i use with a tascam 238 and I really enjoy working with the mixer, it's a beaut
So the hardware setup would be as such:
The M1508 is a 4 bus mixer. So hook group outputs (up the very top of the M1508) of the mixer into the 4 inputs on the back of the a8 (hooking 1->1 etc.).
Then hook up the 8 outputs from the a8 labelled 1->8 to the "tape in" rca jacks on the m1508 (just infront of the group outputs!).
I'd recommend getting some snake/multicables to hook the two machines up just for the sake of neatness and not having cables flying avout everywhere.
Also, download the m1508 user manual and familiarise yourself with it. Same with the a8. The m1508 is what's known as an "in-line" mixer. They can sometimes be a little confusing at first but once you know how they work you will be SO happy that you got one of these to work with a tape machine. (if you can't find the manual shoot me a message I think I have it).
These two pieces of equipment are very well suited for eachother and will let you record quickly and with ease once you know them well.
this setup will let you record 4 separate tracks on the a8 at the same time.
Anymore questions don't hesitate to ask.