Looping in Soundforge is possible, I don't know exactly what you're doing but zoom in and chop off the beginning and end so you're left with the loop. You can even edit Acid properties on the loop if you so desire....

You could also try propellerhead's Recycle.

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In soundforge, cut the wave right before the first beat (kick or whatever), count the beats, and cut the wave right before the ninth beat. If you know the bpm of the track, you can easily timestretch it to fit with the tempo of your choice. If you drop the loop into fl, it should detect the bpm for you, and strech it so it will loop perfectly. I dunno about the SQ of that, so maybe it's best to timestrech it in soundforge, wavelab or whatever wave editor.
It's important to be 100% presise about the cutting of course. Cut as close as you can.

if you know the bpm and it's easy to get it
you can just load the song in Acid and use the snap to grid features so you can easily put loop marker on those 8 bars you like and then use -> File Render -> Loop Region only

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