Think of it as U1 and U2 get grouped together and U5 and U6 get grouped together.

If you have U1 and U2, both 2716 sized files, then they get combined together and placed in U2.

If you have only a U2 2716 sized file and there is no U1 file, then you would double up U2 and its placed in U2.

Same thing with U5 and U6. If both 2716 are present combine together. If you only have U6 it gets doubled.

2kb file is 2716
4kb file is 2732

Converting all Bally/Stern MPUs to take 2732 at U2 and U6 makes the most sense. Max ROM sizing and then is backwards compatible with any game as long as you fill up both ROM chips properly.

A dc powered USB hub also seems to work. I had one of those with my laptop for a while and using it let the gq-4x program the 25vpp chips without issue where I would sometimes have issues plugged right into the laptop and no external power supply.

I have a TOP3000 too and it does a voltage check which is kind of nice. If you try and burn and it thinks the voltage is too low it warns you to connect an external power supply or use a shorter in length USB cable. TOP3000 will not do 25vpp chips tho, so don't recommend it for 2716/2732 despite the documentation listing those chips. Reads them OK, but no burning. Mainly got the top3000 for a dip42 EEPROM I wanted to use.

The gq has a built in verify feature. Set the chip profile. Load the binary file. Click verify icon and it will compare chip data to the currently loaded file in the "buffer" as the software calls it.

Can also check the crc which is displayed in the software near the bottom. Compare crc of loaded file to what you read off the chip.