Welcome to the forum. What speakers/amp/horns did you get?
You don't have to flash the radio to add rear speakers. With line levelers the difference between flash and no flash is the amp can get input from the front and rear output of the HU (flashed) or the amp uses the same input from the HU and just splits it for front and rear channels (not flashed). I have zero experience with the DSR1, but inputs are inputs so the options should be the same.
Some folks have tried just the flash to flatten the HU signal with mixed results. Most guys are using line levelers (not the same as LOC) and the guys that are really serious about the unicorn hunt are using DSPs.
Freedom isn't free, remember to thank a vet.
2018 CVO RG lava orange, 117 Stage 3, 14" F47 and a few chrome extras. Boom crap gone.
2016 RG Special Cosmic Blue, 120ST with Dragos 2:1 and TTS tuner, FBI drop seat kit and JNR air ride. Stock audio long gone.