It was the closest thing I saw in the manual.
My thought was if you could start each component at a volume level you like to equalize the different sources it still may be useful OP's. He did mention the (obsoleted, see below) source level adjust. But, as you an TLS mentioned, it's not clear exactly what the problem is.
I used to have an Integra 40.2, which died of the Onkyo HDMI problems. Just post warranty, of course. It had input level adjustments. Still have the manual on my computer. They called it Intellivolume. Googled Intellivolume and they say Onkyo removed it. Seems like an odd thing to get rid of.
Also, looking at Gene's review on this site:
Integra DRX-4.3 9.2 Channel AV Receiver Review (audioholics.com)
It may be worth seeing if the Integra PC Setup App is now available to the user. According to Gene, "The setup features are extensive and allow you to tweak everything in the AVR..."