First, just because an unnecessary process is running does not mean it's impacting your ability to record and mix music. If you're able to do everything you need to do at the required latency, then leave the O/S alone.
[Note: beware the widespread but illogical obsession with achieving the lowest possible latency. Low latency is really only needed for playing soft synths in real time. For mixing, editing, mastering, tracking live audio and recording MIDI from outboard sources, latency is a non-issue. If you're not tracking soft synths in real time, set the latency as high as you need and forget about it.]
Rather than preemptively killing processes that might affect DAW performance, and thereby risking accidentally disabling something important, it's safer to approach it from the other direction: find out what's impacting performance first and work backward from there. And by performance, I mean just one thing: the ability to use the DAW at the required latency without dropouts. Beyond that, there is no benefit to further tweaking.
Start with the Windows Task Manager. Look for processes that have allocated large amounts of RAM (some processes can gobble multiple gigabytes of memory) or that show high CPU usage. Then look them up and find out exactly what it is that they do. That will inform you as to whether or not they can safely be disabled. If they are a background service, stop them but don't disable them. That way, if things go horribly wrong you can just reboot.
For example, one of the services that SONAR (and your audio interface's driver) relies upon is Windows Audio. If you stop it, audio devices will not be recognized and you'll get no sound from any application. Less obvious are service interdependencies, services that rely on other services to run. For example, the Windows Audio service depends on the Plug And Play service, a non-obvious dependency that might seem to be a candidate for shutting down. Microsoft doesn't document such dependencies and they can change from one version of Windows to the next.
If you examine the Task Manager and find no processes that are hogging memory or CPU, but still have issues with dropouts, then the problem's likely something that's not reported in the task list: ISRs, DPCs, bus contention, IRQ conflicts - IOW, hardware. It may come down to using the wrong hardware (e.g. a gaming video card) or even a broken interface, but taking the problem hardware out of the picture may be as simple as stopping an unnecessary service. Topping that list would be network-related services, especially wireless network adapters.
I just read back what I've written and realized that my reply is largely off-topic relative to the OP's question. Oh well. I should have my morning coffee first, then babble, not the other way 'round.