normally while tracking, I am using a small buffer size with no latency. When it is time to mix or apply reverbs, delays and other processing, I open the preferences and increase the buffer size. occasionally, immediatly when i do this, all audio stops in sonar. My interface is also a controller and the controller stops working as well. however windows media player will produce audio using the interface. So it seems that windows still sees the device and it does work within windows, seems like Sonar just doesn't see it any longer. I have to reboot when this happens. Doesn't happen very often. I do have the latest drivers and updates from tascam.  What else can I do to determine if this is a sonar issure or a non sonar issue?

This happens to me every time I change the buffers on my M-Audio Fast Track Ultra.

There's a whole process I have to go through.

The only difference is, I don't have to reboot like you do.

I get an error message about an 'Audio Dropout', then I get an error message saying "No audio recording device", then I click ok, play the project again, and it works.

Don't laugh (LOL), but have you checked Tascam's web site for a firmware update to your unit? LOL!

Sorry for laughing, but this is one of those rare cases where that may actually help if there is one available.

Firmware is the internal software on the chips inside your unit. Since your drivers are updated and you still see this, it may be a chipset software (AKA Firmware) problem.

I went thru the firmware discussion over the last few days. I did check my driver version, I will look again to make sure. 

I make a big distinction between updating the firmware for a device and updating the firmware of a motherboard.

By all means if your device has a new firmware update available, go ahead and update it. Just follow the instructions :-)

That's normal. You are changing a pretty important setting that effects your project. I don't know the technical ins and outs of it but I'm assuming the hardware needs to separate itself from Sonar's audio engine briefly to make the adjustment. The same thing happens to me but it's a very brief engine shut down. However I usually save my project, close it then make the changes to my interface settings. Then I'll open the project back up. No biggie.

There is a "Stop Audio engine" button in the transport area. Clicking that may help avoid this issue. I just save, close Sonar, change my setting and re-open Sonar. It seems to make life much easier.

Are you using the Tascam & the Presonus at the same time?

Or are you just using the pre-amps in the Digimax

If you're running under ASIO and also running 2 interfaces, you might run into problems like this, so either eliminate one from the system or change driver mode to WDM

What else can I do to determine if this is a sonar issure or a non sonar issue?
 

This is very likely a non-sonar issue. I changed latency (i.e. ASIO buffer sizes) around a lot during recent stress testing of the new DAW and also earlier with the old DAW when I was using a much slower CPU, but never experienced any issues like that due to changing ASIO buffer size; I'm using different interfaces, though, but all Roland ...
 
<<I had some sonar crashes with other operations in sonar that did not free up the audio drivers until a reboot, but these crashes have become very sparse since X2a>>

What the OP is attempting to do is quite a common strategy, and one I use myself in virtually every project, once it goes beyond a certain size/complexity.

I was going to ask if Traceystudios was trying to adjust this with the project running, but you can't open Preferences unless the transport is stopped, so it's nothing obvious.

Bristol: I am actually just using the tascam alone, I have an preamp I run thru before I hit the interface. And I am not sure what you mean by "project running".  I finished recording a track, hit stop, edit/pref..changed asio buffer size etc. clicked apply, then ok. and my inteface no longer responded to the controller. I clicked play, Sonar started to play however no audio was hitting the interface.

GuitarPrima: I have tried to toggle/restart the audio engine and still doesn't work. the tascam has its own control panel for windows and it shows as connected and windows media player can still see it. Just sonar can't. a reboot and all is good again.
I have tried several thing to avoide the reboot. just haven't found the right one yet.
I have adopted the save frequently method. I am constantly saving the project because of llittle things like this. I wish there were a save button on the toolbar. I know I can hit a key combination, but the button would be really handy for my habits.