One reason that people like to go with separates is that a standalone amp typically has a larger and more robust power supply - allowing such amps to work much better with difficult loads and to react to sudden and/or significant demands placed upon them. It ends up not so much relating to how loud you can get as how it sounds at the same volume level. A separate amp also helps with the "upgrade bug" because it lets you get a good amp that you like and keep it even if you find yourself replacing the pre/pro. If you already have the 7100, I'd probably at least compare the two (1070 as pre/pro with 7100 and 1070 by itself) before parting with the 7100, because you may want to keep the 7100.