Doesn't the MC1488 invert the signal? So when the MAX7219 drives high on the DIG lines, you end up driving the DIGx pins low?
And the same for the ULN2803 - when the MAX7219 drives high on the segment lines, the segment lines get driven low?
Let get the facts about the MAX7219.
Hardware : The segments are : a, b, c, d, e, f, g, DOT A HIGH / 1 is generated from those segments. <--- see commun cathode
The digits are a LOW / 0 when a digit is selected. Because a HIGH to LOW will flow the current, but a HIGH to HIGH will not.
So let get this principle in mind. To drive a bigger currents - leds type, let look at a commun anode type display, so you simply apply the same principle.
I don't know what is the type of config your display is commun anode or commun cathode. Until you know the config, than let figure out a way to use transistors / drivers to control more currents to use a HGH - LOW <-- MAX7219 principles first. As long you are aware that principle, than your code will work. ( in theory ) 
And one little trick here, use an INVERTER gate if you have too, that solution may work.
An NOT gate --> 0 --> 1 or 1 --> 0 See the 74LS04. Just use a octal NOT gate.
Software : The MAX7219 have a Decode Mode Register = 0x09 A No Decode : Can display what ever you want from the segments. Check the datasheet. page 8. Example : Let display 01101100. You simply send this data into the register data to be display.That is good for leds matrix. Code B will display according to Table 5. The register data is simply a number from 0 to 9 and it will display a number according to table 5. But the digits being selected , well, a LOW will "select" that digit by sending a LOW. So you are stuck with this.
I am sorry you may have to re-design the circuit to accominate the 7219.
@CrossRoads The max7219 i believe sinks the current in the Digx. so when it is hooked up to the MC1488p line driver, it will invert it, and supply the 7-segment with the 12 volts at Vcc.
Also here are the 7-segments that i got from sparkfun.... 7-Segment Display - 6.5" (Red) - COM-08530 - SparkFun Electronics
ill have to take a look at the decode mode register too... i am using the ledcontrol.h library, ill have to figure out how to write to registers for the max7219
Okay, you're using a common-cathode driver to control a common-anode display.
You're sending the high-output segment lines into an open-collector driver, the MAX7219 high-out creates a low-output from the ULN2803.
Youlre sending the low-output digit control lines into an invertor trying to push current into the cathodes of LEDs.
You need to read this application note
http://pdfserv.maxim-ic.com/en/an/AN1196.pdf
to use the MAX7219 with a high-voltage common-anode part.