If your only running two lines from your keyboard I don't think it would matter. But having everything plugged into one unit and using the stereo link is more convenient. You don't mention if your using an outboard mic so in that case using one unit with keyboard and mic is the way to go. Keep the master unit near you for easy adjustment although once I set mine up in my studio I haven't had to touch the settings for a long time. Just run them flat and then EQ a bit from there, don't need much. They are amazing little units and really hold their value.