Without re-installing anything, make a folder "ASIO Unused" under the application's folder, and drag all (3) ASIO drivers into it.
Then one at a time, drag a single ASIO driver in the correct ASIO folder for the application and test. (Make sure that only 1 ASIO driver is in the main ASIO folder at a time).
Also, avoid routing the "system sound" in OS9 to the 2496 while testing.
You can do this without rebooting and as far as buffer size try 256 or 128, the lower you go the less latency while using a keyboard controller, but more demand on CPU, there is no "optimal" setting. So, always the same rule, while "recording" and/or sequencing with a controller, set the buffer to the lowest setting you can (128,64,etc) without the mac overloading; for playback and mixing, switch back to 512 or larger, all tracks will play in perfect sync even with large settings, less strain on CPU.
Lastly, I don't remember which ASIO driver I used in the V2 package for the 2496, but I remember having to use a different ASIO driver with the Sonic powerbundle, than I used with CuBase. It is always trial and error, but it should be very easy and fast to switch and try them each per application. It all comes down to the ASIO spec (V1,V2) and what the programmers tweaked at the time they wrote the app.
Oh... one last thing, as far as sample rate, unless you are doing film, stick with 44K, the reason is simple, if you decide to you use loops/sample libraries or external media, most are recorded at 44K and you can just drag them in... you can mix 16-bit, 24-bit and 32 bit audio (all at 44K) without issue. The general rule here is that if your track does not sound good at 44K 24-bit, then delete it, no higher sample rates can fix a garbage track. That being said, 24-bit audio holds up much better than 16-bit audio during mixing as you have more headroom (volume choices, effects processing, etc.) since you have a lot more numbers to work with. The idiots that say "just record and mix at 16-bit, since you dither down later anyway... right ?" obviously don't "mix" in the DAW or they would notice the "headroom" thing I mentioned right away. At any rate, 44K, 24 Bit audio will yield pro results if recorded with a decent interface, at a decent level.
And one more thing to the last thing, This "Instant DAW" was created with all 2496 drivers ready to go, maybe you'll like it.http://macos9lives.com/smforum/index.php/topic,2716.0.html