Dimension Pro Midi Out Softsynth

Are you using Dimension Pro in a DAW like Sonar or is it the standalone version of Dimension Pro?  The reason I ask is because the options are different.

Anyway, the problem is in part due to the question you are asking.  However, it is obvious to me that you are having latency issues.  

The MIDI Inputs/Outputs of your USB Keyboard should be selected, not the MS GS Wavetable Synth.  Next, make sure the correct audio device is selected as well as the proper audio drivers.  Once that is done, select the highest sampling frequency your soundcard can handle and lower the sample rate to the lowest number possible without hearing any clicks, pops, distortion, or degridation of sound quality.  You may just need a better soundcard.
 
Let me know if you are using Dimension Pro as a standalone or in a Cakewalk DAW.  I'll walk you through the process.

You have a good soundcard.  However, I'm positive the delay is coming from your soundcard settings, either in Capella or the program that came with your Audiophile 2496 or both.  Change the settings like I stated in the earlier post.  I have an Audiophile 2496, but I am not familiar with Capella.  

The MIDI Out is irrelevant to the delay issue.  The reason you only have MS GS Wavetable Synth for MIDI Out is because your USB Keyboard must not except MIDI In.  Maybe confusing, but MIDI Out of something goes into MIDI In of something else.  If you need a MIDI In/Out to another program try using MIDI Yoke.  It's free and what you are asking for.

I just got through looking at the Capella site.  Now, I can see what is going on.  In the "Playback Devices" tab in capella-tune, set "Wave Out" under "Wave Output for VST Devices" to ASIO, which you probably already have done.  Now, click the "ASIO" button.  If it is like most "ASIO" buttons it will bring up the Audiophile 2496 soundcard settings.  Make the sampling frequency 96khz (the higher the sampling frequency, the less latency/delay) and the sampling rate 128 or 256 (the higher the sampling rate, the more latency/delay).  That should take care of your latency/delay problems.
 
I just thought of what you might have ment when you refered to a MIDI Out softsynth, after viewing the Capella site.  MIDI Yoke does not make any sounds.  It only patches MIDI from one place to another.  A VST instrument, like Dimension Pro, on the other hand, does make sound.  The confusion comes from the way Capella has setup their "Playback Devices" tab.   By the looks of the Capella site, if you installed a VST like Dimension Pro, then it would show up in the MIDI and VST Output box.  By selecting it you would hear sounds from Dimension Pro.  What is really happening is MIDI is coming in from a source, like Capella or your keyboard, and is sent out to the VST instrument like Dimension Pro.    Capella has just confused everything because they put the MIDI Outs and VST's into the same box.  There is no such thing as a MIDI Out softsynth.  They should have set it up with a MIDI In/Out section and a VST section. 

Trying to learn a little more as I go.   I was having distortion/latency problems playing Dimension pro via a Edirol keyboard.  I went to the Audio menu and adjusted the buffers to 60. msec (was at 2 went to 3 on playback and went from 20. to 30. on buffer size)  seems to have fixed the problem.  How does buffer interact with sampling?

Stumbling carefully here.