According to my calculations 1 lbs dextrose is equivalent to 0.91 lbs spraymalt as far as the OG is concerned. I'd use 2 lbs of spraymalt to replace 2.2 lbs dextrose.
If you replace the dextrose with extract, you will increase the FG a bit, as the extract is not fully fermentable, while the dextrose is.
There are only 10 types of people in this world. Those that understand binary, and those that don't.