Funny asking for help with Studio One here in a Cakewalk forum, but after spending hours searching the program and the internet this is the only place I can think of.  Presonus online help is not very helpful.
 
I'm trying to set a song, or project, or whatever to a sample rate of 48k going through the onboard Realtek HD Audio.  I have other interfaces but for just puttering around, it's simpler just to use windows sound.  Studio One only offers me the option of 44.1K with windows sound even though the Realtek is set to 48K in and out (and apparently doesn't even support 44,1K for 'Stereo Mix').
 
In Sonar Platinum, everything is so easy.  The Realtek is visible and I can choose from several different driver modes WASAPI, MME, WDM/KS and sample rates, including 44,1K and 48K.  I can find no equivalent configuration options in Studio One to select the different audio modes, for any of my interfaces.
 

You have tried everywhere except the place you should be e.g. the Presonus Forum!
 
Here:
 
https://forums.presonus.com
 
Now I have a Mac and a PC setup and I have just checked the Mac and yes it seems it offers only the 44.1K option with its internal audio. But it works though. So what happens when you play sound out to your sound card and it is set at 44.1K. For me it still works fine. That is all that counts really if you are just wanting to hear stuff.
 
I am not near my PC at the moment but will check. I must admit I have disabled the internal audio on my PC because I just never use it. The latency is way too high and the quality is average as well.

Something to think about would be ASIO4ALL. As much as it pains me to say this, when I loaded Samplitude, the MAGIX ASIO Driver (which is ASIO4ALL with a different faceplate) ended up solving my woes when shifting between my Saffire and the RealTek in Studio One. For some reason, Studio One has issues when doing that manually, but it shifts rather easily using ASIO4ALL.
 
ASIO4ALL is sort of a mind-trick to "whatever" software making it think it is in ASIO when it is actually using WDM drivers. It also seems to intercept a lot of the "micromanagement" software tries to do. As far as the DAW is concerned, it is using the proper driver and the proper sample rate. I have found a couple programs that will actually "lock" ASIO4ALL to them, so just avoid those when working (or turn them on after Studio One, so that Studio One got it first).
 
As much as I wanted to stomp that MAGIX ASIO driver into the dirt, I also have VSTis that run in standalone mode and require ASIO. So after tinkering with ASIO4ALL (I had a really bad initial experience with it years ago), it has found a purpose for when I want to do something quick (i.e., only power on a MIDI controller versus turning on everything else too).
 
I have put S1P 3.5 into a boot loop (startup/crash it) twice now shifting between my Saffire and Realtek, and forget how I broke it loose offhand.

i would not mess with the realtek,
at all,
if i had other options.
 

For playback, there is nothing wrong with the RealTek chip; but you cannot record (quality) audio through it.

mettelus
For playback, there is nothing wrong with the RealTek chip; but you cannot record (quality) audio through it.

^^^ THIS

From the OP he does not want to record. Tip: Read the OP! He just wants to playback. From what I can tell Studio One will playback fine through any internal sound card and that is all he wants to do. 
 
But I also think playback quality is best served with a better interface, even a small one.
 
Not sure why people get flustered over 48K. FACT: 48K does NOT sound any better than 44.1K. So lets put that to rest. The only people that need to be concerned with 48K sample rates are those producing music for film or TV because for some reason in that line of work they have chosen 48K as the default sample rate. ( I do a lot of this so I start sessions at that rate) 
 
Its best to do everything at 44.1K 24 bit for sure but start and end everything at 44.1K. If you have to burn a CD for example no sample rate conversion required, only dithering from 24 bit down to 16 bit.  

many plugins work better at a higher sample rate,
with less latency..
 
so, if you are talking about playback, you still have to consider sample rate.
 

batsbrew
many plugins work better at a higher sample rate,

 
Sorry but not 48K compared to 44.1K. Yes for sure with 96K compared to 44.1K. Big difference compared to tiny difference.
 

yep, that's what i meant. higher rates.
usually cuts down the latency of the big dogs in half.