Before you put down money for drumagog, I have a suggestion.
It may get you what you want and it may not, but it won't cost anything because you already have everything you need.
I'm assuming that you already have the drum samples you want to use. If so, all you need is Sonar, your dr-008 plugin and your original waveform.
Let's say you want a new kick sound. Take your kick track and roll off all the lows and boost the upper mids a bit. This step isn't really necesary but can help you achieve "cleaner" triggering.
Now your kick track is going to sound absolutely horrible and more like a weird click than a kick, but this is okay. All we really need is the attack from the kick and nothing else. the peaks in your waveform should now look very short. Every hit should look pretty much like a vertical line.
Now for Sonar's secret drum replacement tool that I rarely ever see talk of. I haven't used it in a long time so my memory is a bit fuzzy, but select your kick waveform and find the "extract audio" funtion (I think it might be under the edit tab, if not, keep looking, you'll find it along with the "reverse" and "make 3db louder" comands if I remember right.)
An options window will pop up with sort of a threshold setting. Any audio peak above the treshold setting you specify will be transformed into a MIDI note (you can also specify the note) and will be saved to your clipboard after you click OK. I think if you hit "audition" you should see little marks on your timeline above the tracks pane which represent where the MIDI notes will go. Check to make sure they line up with your waveform's kick hits and click OK.
Now insert a new MIDI track, select it, and hit CTRL+V (paste). You should now have a MIDI version of your kick track. The Extract Audio options box also gives you the option to keep your dynamics (in MIDI velocity form) according to the waveform or to set all MIDI notes to one common velocity. Thats up to you wether you need to keep the dynamics or not. (you can adjust the velocity of each hit independently if you have the spare time for it).
Now that you have the MIDI kick track, Mute the original kick and insert a new audio track. Insert the DR-008 plugin here and load it with the new kick sample that you want. set the MIDI kick track to control the DR-008 plugin and you have yourself a new kick without spending a dime.
For more realizm you can probably use dynamic multisamples if the dr-008 plugin supports them, but I dunno, I use battery myself.
Anyway, give that a shot and let me know if it works. If, not, yea drumagog will probably help you out.
I hope that all made sense, and I'm sorry my memory is a bit fuzzy on the details.
Edit: I just re-read this thread and realized you said that the track won't vary in volume at all, so you can just forget all the stuff about dynamics, this technique should wourk perfectly for you.
