I have been trying to correct for latency playing through the Presonus AudioBox. Somewhere in this forum I read that I should be using the ASIO drivers, which my sound card did not support. I purchased a sound card that does (Xonar DS) and installed it, and made sure that I have the latest drivers from Presonus. Now I'm having difficultly getting the functionality back from AudioBox. I am given the option to choose either the Xonar drivers or the AudioBox, of course, I need to be playing through the AudioBox. I did not get the AudioBox ASIO option before, now I do, looks great, but there are two problems. I no longer get the AudioBox Headphone option, so I can't route to my headphones, and when I go into record I get this message: "Unable to open audio record device. Device may not support the current project's audio format or may be in use." Any idea what I did wrong or what I'm missing? (Also, I've been trying to get help from Presonus, they are not very responsive.)

AFAIK, Presonus has always supplied ASIO drivers for their products. Make sure both the ASIO mode is selected in preferences then select the Presonus interface in preferences. The ASIO specification will only allow one driver to be used at a time so if another interface is selected in SONAR, it will be necessary to deselect both the input and output of the other interface before the Presonus will be available.

I haven't been able to find a specific "preferences" in Sonar, but under Audio Options, I have AudioBox ASIO driver selected everywhere it is possible and offered. That includes Playback & Record Timing Master, the Driver Mode, the Record Latency Adjustment, and under Drivers it offers me all the sound card options, and the AudioBox ASIO, I have only the AudioBox ASIO selected (of course, it will only allow one of the other). If you're talking about Global Options, I don't find anything called Presonus Interface, if you just mean select AudioBox, I can't find anymore references to it that I haven't selected. And again, when I call up a file and try to choose the Output route, I no longer get an option to route to the headphones.

This must be an older version of SONAR LE, there have been several. If the Presonus AudioBox works like other Presonus interfaces, there would be no dedicated route to the AudioBox headphone output in SONAR. There would only be output options for "ASIO AudioBox line out" which drive the main and headphone outs of the interface. The headphone volume  is set at the interface.

As far as I know, only one audio device can be selected at one time. If you had a built-in audio card, then you would have to disable that to use the one you prefer. I would wonder why you need a second sound card when the AudioBox should handle all of the sound for everything, including Windows Media Player and utube or itunes or anything that you play music through your computer. The only time you are using the ASIO drivers is when in Sonar, and in Windows have you checked your speaker icon to see what is marked as playback and recording (by right clicking on the speaker icon on your task bar - if showing it - by getting up Control Panel -> Sound, Game Controllers whatever it is and checking there if need be (same thing as right clicking on the speaker icon on the taskbar) and  making sure the Default is marked for the AudioBox and that is listed as Recording and Playback on that for Windows, (or just checking to see what is listed there - usually the graphics drivers may have HDMI listed there also in case you use a HDTV with that connection which carries the sound and video from your computer to the HDTV).
 
As far as I know - only one sound device at one time in the computer - either one or the other with the one not being used Disabled in Control Panel -> Device Manager which can be found by right clicking on Computer desktop icon and right clicking and selecting "Properties".
 
With that and ASIO drivers for the AudioBox all the sounds are going to that unit and the headphones should work on that unit - unless there may be something wrong with it.
(but nothing working on the other sound card that is not needed unless switching to it and disabling the AudioBox then - one or the other).
 

Before getting the new sound card, my interface between the AudioBox and the computer was working just fine (I mean, working just fine other than the latency problem), I could choose all tracks to route through the built-in sound card when I wanted to hear the mix in the air, or the AudioBox when I needed the headphones for recording. Right now, I have no option to choose the sound card, and I can't tell whether the output is routed to the headphones (which I guess just means being routed to the AudioBox) because hitting play only gives me this message: "Unable to open audio record device. Device may not support the current project's audio format or may be in use." (It is an older version, LE 8.5.1.17) Also, checking the Windows Sound device options... for playback, the AudioBox only appears as the "default communication device" which I have selected, and in Recording, it only appears as the default Line-in device.
 
Just to be clear, I am currently unable to use Sonar because of that message, I cannot record anew or playback previous recordings. If I change the drivers to the new sound card, I can playback and go in to record, but of course, my keyboard and mic need the AudioBox, which they no longer have access to...

Is it possible the Audiobox is setup as the Windows default device? If so, make sure to select a different device for Windows. Is another application using the Audiobox while SONAR is running? If so, there may be a sharing problem.
 
There will be a difference between using ASIO and other modes in SONAR. The previous setup was using either MME or WDM which can handle multiple drivers and devices at the same time.

Well, RealTek was the built-in sound device, all those options are disabled. I have the new sound card (Xonar DS) selected as the default device for playback. For recording, the only place the AudioBox shows up is "Line-in", which I have selected. I don't know if that is correct, seems funny to me.
 
So, if I'm using the AudioBox, and I'm done recording, and I want to hear the playback in the room, how am I supposed to do that if I can't choose the sound card for Output? I am only becoming more confused I think. There must be some basic, simple step I'm missing here, but I just can't find it. As far as whether another device is using the AudioBox... nothing I can think of, nothing that I've chosen, I don't even know what would.

A few things to consider. ASIO mode will only permit one driver at a time to handle both input and output in SONAR. It is possible to switch driver modes and/or devices as long the device chosen supports the project sample rate and bit depth. If the device does not support the project sample rate or bit depth, SONAR will through the "Device may not support the current project's audio format" error.

Lol, okay, so if I don't use ASIO drivers I can't adjust for latency, and if I do use ASIO drivers I can't listen back to my mix in the room without going into Windows every time and changing the default device...
 
How do I find out what the proper project sample rate and bit depth is and where in Sonar do I adjust that? Right now, in the Audio Options, the sample rate is set at 44100. In the Global options under Audio Data the bit rate is 16, and the render bit depth is 24. When you say "device chosen", I assume you are talking about the AudioBox?