From the Peavey website:
TNT 115
* 200 watts (rms) into 2 ohms
* 150 watts (rms) into 4 ohms
* 1/4 inch input jack
TVX 410
* 8 0hm
* Improved crossover for better midrange tone
* Vents located on front of cabinet
* Horn tweeter with level control
* Protection circuit for horn tweeter
* 350 watts (rms) continuous
* 700 watts (rms) program
* Four 10 inch Sheffield® bass speakers
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Looks like the TNT is setup to run a 4 ohm extension speaker to get the max watts.
If you run the 8 ohm 4x10 you'll get 2.67 ohms.
It'll still work but the volume may not be balanced between the cab.
Maybe the 4x10 can be rewired to be 4 0hms.
Try it out the way it is and see how it sounds. Go from there.