Technically speaking, the best tool to use would be a Music Creation program like Acid Music Studio, Acid Pro, Magix Music Maker, Magix Samplitude, etc...
All of these programs use multiple tracks, so you would just add the cymbal crash onto a track above, at the points it needs to be.
Sound Forge is not really set up for creating (constructing) original music.
Sound Forge is for Editing, Cleaning, Mastering, etc...
The solution I would use for a one off project
However, if you have Vegas Pro or Vegas Movie Studio, you could use those programs to do the same thing.
Vegas can be used a Music creation program as well - it's not limited to only Video creation.
In Vegas you can render/output to .wav or .mp3 audio file only.
Remember to turn everything off at least once a week, including your brain, then sit somewhere quiet and just chill out.
Unplugging is the best way to find solutions to your problems. If you would like to share some love, post a customer testimonial or make a donation. Peace 
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