Excuse me if you already know the following, but you have not mentioned that in OP:
1) MIDI produce no sound by itself. MIDI should be interpreted by some synth for that
2) there are hardware and software MIDI synth
3) Windows historically has build in software wave table based MIDI synth which it exposed AS hardware synth to all programs. It has worse quality and latency from all available variants, also it always use Windows mixer for output and so it can not be used in parallel with ASIO (on the same hardware). The first you should check is that you have disabled it in Creater. Check Preferences/MIDI and de-select all output MIDI ports not related to your Oxygen (to avoid MIDI files opening problems, de-select ALL MIDI outputs).
4) you should use some software synth inside Creater. For General MIDI files you can use TTS-1. It should be used by default when you open MIDI files and have no MIDI output devices, but that is worse to check.
5) software synth generate audio, but it still has to be delivered to the hardware. There are several "routes" between a music program and the hardware, Creator support all of them:
5.1) MME. Most compatible, mix sound coming from other programs and convert bitrate when required. Due to the nature and required processing, introduce latency and produce bad output quality. There target is to use as less computer resources, and so they scarify the quality and use huge buffers (smaller buffers == more work).
5.2) WDM with KS (Kernel Streaming). KS is used when you select WDM, the driver support KS and the audio information is "compatible". You get less/close to no processing and so improved quality and lower latency. No mixing with other programs possible.
5.3) ASIO. The only target is to deliver unchanged audio stream to the hardware as fast as possible. No mixing, no volume control.
5.4) Pro. music audio interfaces have specialized ASIO drivers. And that is the way to go once you have one of such interfaces
5.5) Consumer audio interfaces (build-in Realtek chips) have WDM drivers only. When everything setup correctly and the driver has KS support, the performance is not so bad. Unfortunately, it is easy to step one mm from the route and fall back to "normal" (processed) WDM scenario. And so:
5.5.a) ASIO4ALL is an intermediate driver, which tries to get the best from existing WDM driver and deliver to user programs "ASIO" interface. It works inside the kernel and so have more options to talk with WDM then user program (Creator). Depending on many factors, you can get even less latency then in WDM/KS scenario and that is normally easier to achieve then (blindly) attempting to make WDM/KS work properly. But that is not "plug-and-play with perfect results" solution. You still should find good options inside ASIO4ALL control panel and Creator settings. There are tons of information in the Internet, but carefully filter it (most people do not understand the topic, either describing ASIO4ALL as a "voodoo" or as a "audio killer").