Hi 616marek! The first thing I would recommend is to try connecting to input 1 instead of input 2, just to see if that makes a difference. If you notice, input 1 says MIC/LINE under the connection. This is referring to the impedance types that the input is designed to accept. Your Casio is more than likely outputting a LINE LEVEL impedance output, which would need to be connected to a LINE LEVEL impedance input. The center of the INPUT 1 connector is designed to accept a balanced 1/4" connection. You will also need to experiment with the GAIN 1 knob to get the level correct. As for distortion and crackling happening when playing back audio from the computer, the issue could be with the ASIO driver and how it's reacting in your operating system. One possible solution would be to try uninstalling the ASIO driver, and then installing the specific Behringer driver that is downloadable via the following DropBox link: https://www.dropbox.com/s/1x4g21ed44wuhke/BEHRINGER_2902_X64_2.8.40.zip?dl=0 I hope this gets you going in the right direction and please let us know if you require any further assistance.
Hi McElviss! I'm not sure if you've gotten an answer to your question yet, but I would not expect the SPL between these units to be drastically different, especially since they use the same amplifier specs. I, unfortunately , do not have the exact SPL numbers available to me. However, the only difference that you might notice is a slightly lower frequency response from the B115D, as the B115D has a frequency response range of 45 Hz to 20 kHz, while the B112D has a frequency response range of 50 Hz to 20 kHz. I would suggest that if you are only concerned with a single vocal, some guitar, and possible a kick drum, then the B112D should suit your purpose perfectly fine. I hope this helps for you.