I have owned a GNX3000 for several years now and never connected it to my PC until this weekend and ran into a few issues with it. I went and grabbed the newest drivers, loaded it all up and then jumped into X3c with it...
 
   1) When running ASIO mode (USB) with it, the ASIO panel will not "take" for the two lowest settings. I can set it there, but when I click "OK" and reopen it, it always resets to the middle value (10ms, I believe). While trying to troubleshoot this, I got X3c to crash.
   2) It comes with software (X-Edit 2) which will allow me to program a patch directly from a GUI, so I do not have to deal with tweaking buttons on the unit. This would be nice to run while recording, but when I set my new Saffire PRO 24 to ASIO and ran line outs on the GNX3000 to the line ins on the Saffire, the latency was even worse (the Saffire has been like grease lightning so far, so the only thing I could think was the USB). I unplugged that and it still did not go away.
   3) When I first used it in this manner through the Saffire (no USB or ASIO switching in X3) it was very fast, so not sure why this "went away."
 
   I was looking at the manual, and it seems the GNX3000 may run USB 1.1 (it says it supports 2.0, but will run a 1.1 protocol), which might be the explanation for #1 above.
   As far as #2, I do not understand the sudden latency with the Saffire in ASIO mode unless perhaps the X-Edit 2 software is talking to the unit... BUT... I was running the line outs to a monitor system while adjusting patches and had no latency, so am baffled.
 
    Does anyone have insight into what could be causing this?

Maybe the clock timing between the two. (Two different settings).
Also look at the Saffire mix control settings and routing .

I know that for my Presonus audio interface that the range of allowable ASIO Buffer Size choices is limited by the Sample Rate, so if I am running at 48k Sample Rate I cannot set ASIO Buffer Size below 64.  (I use 128)  At 44.1 k I could go down to 32 for the ASIO Buffer Size.  Each interface vendor does things a bit differently, but all kind of work the same way with ASIO, more or less.
 
Some interfaces control the ASIO Buffer Size using Number of Samples, or have choices for buffers using Milliseconds, which sounds like what you have.  My interface Buffer Size setting of 128 at Sample Rate 48k corresponds to about 4.7 MS or 224 samples.
 
Also, you MUST have the Sample Rate settings in Sonar exactly match the Sample Rate settings for the audio interface.
 
My own settings, which work well for me, are:
 
Audio Interface: Sample Rate = 48 k, ASIO Buffer Size = 128.
Sonar: Driver Mode = ASIO, Sample Rate 48 k.  
 
Resulting latency values in Sonar are: 
 
Input: 4.7 ms, 224 samples
Output: 4.7 ms, 224 samples
Total Round trip: 9.3 ms, 448 samples
 
I have gone lower on the ASIO Buffer Size, but then face a bit of instability with the sound, so I backed it off to what is listed above, and this gives me no trouble at all - as well as no audible latency (that I can hear while playing)
 
Bob Bone
 

Thanks for the response! I felt like I was wrapped in spaghetti messing around with this last night so attacked it again today. I got everything to function as I wanted, but went a very specific route to get there which seems to work fine:

1. Setup audio routing only at first. GNX3000 feeding the Saffire in ASIO mode. Without the USB connected, SONAR only sees the Saffire, so latencies are nice and low (65 samples input/94 samples output).
2. Then I connected the USB to the GNX3000. SONAR recognized it and gives the option to add the device now, which is a massive "NO!!"
3. Launched the X-Edit 2 program to drive the GNX3000 with a GUI, and functioned fine with no effect on latency. The unit is still trying to route audio out the USB, but is sending it no where, so doesn't affect latency at all.

   In hindsight, there are two things I did last night that contributed to the latencies I saw: 

1. I have never had much luck with shifting ASIO cleanly from one unit to another in SONAR, and after reassigning things I should have closed/reopened SONAR to get a stable start point (I blew this off).
2. This may be the real issue I created while messing around... To "fill out" mono tracks, I will then post process a signal by setting interleave to stereo, throw VX-64 in the FX bin to apply the doubler, concrete limiter in the PC, and monitor the result with R-MIX. In the process of messing around, I then armed this same track and was recording another quick passage to extend the track (which was still recording mono), so my adjustment of the interleave, then coming back to record a second time may have been throwing SONAR for a loop... that was the point where I was getting latencies around .5 seconds.

   Ironically... this all started from the "DI box" comments in Craig's thread, and I really wish I had connected the GNX3000 to the computer years ago. It has a neat feature in that you can mix and match heads to cabinets, but can also assign TWO to each preset, then "warp" the signal flow between them. The unit has a truckload of buttons, etc. which makes it oppressive to get full use from, but the UI has these all "right there" to be modified in seconds. And with sustain being the topic of most concern, I put new strings on the thickest through-body necked guitar I own (and old Epiphone ES-335) and got extremely adequate sustain results. TH2 and Guitar Rig might be headed to the dog house.
 

I used the GNX4 transport to control Sonar's transport...there was a control surface plug-in for the Pro Tracks Plus software. I think it also works with the GNX3000 but I'm not sure if it works with 64-bit systems or not.

The GNX4 and GNX3000 function very similarly, and that option is available, but I am so not savvy on control surfaces. That unit has been parked in front of a Carvin tube amp for 8 years now, so my first hurdle is getting that audio into SONAR and not having to tweak any edit functions by getting on the floor, lol.
 
One of these days I will have to delve into the control surfaces and get my head around them; but for now, I am relying on my wireless mouse