I shoot several events every year in conditions like this.
Give up thinking you can ight the whole room with one flash.
You need to decide what the subject is and get as close as you comfortably can to document it. A Stofen-type cap only reduces flash power in a room like this. At the distance you were shooting from, at what appears to be the subject, it does no softening. Other than the exposure difference, notice the similarity in your photos? Trying to get fill from bouncing the light using the Stofen, especially with that high ceiling just doesn't work. The light is probably still up there.
Here's what I do:
-As I said, get as close to the action/subject as you can.
-Shoot with the camera on manual and set it, by testing, to get the ambient light about 1.5 stops under exposed.
One venue I shoot in is always dark (to enhance the patrons' looks, I assume) My exposure is usually about 1/15th @ 5.6 with ISO 800. This technique is called "drag shutter". That will help with keepng the photo from looking like it was shot in a cave, which would happen if you used a higher shutter setting. 1/15th of a second too long? Don't worry, the flash goes off at around 1/1000 and freezes the action of the subject. The background is secondary and a little blur isn't going to be noticed.
-With my Nikon flash, I get great results most of the time just using ttl. There are some times when I need manual, like when the people show up wearing all white, which would make the flash underexpose. For the flash, since you're closer, you
can use the Stofen crap...cap, but it's still not going to do much softening. Get a Light Genious Light Scoop. It's bigger, so it would soften the shadows a bit more. Instead of wasting light and blinding people behind you, it uses it to expose the subject.
http://www.litegenius.com/ Now, for a little advanced lesson.
You are using a flash to expose the subject of the photo.
That is about 5000~5500 Kelvin degrees (near daylignt color balance)
The room looks like it is illuminated with incandescent bulbs, usually around 3000 Kelvin, very warm and even more so if they are dimmed. To get them closer in color tempreature, you put an amber color correction (CTO- color tempreature orange) filter over the flash to get it closer to the ambient tungsten light. An exact match isn't needed and I actually like a little warmth in the background anyway. Then you set the camera's color balance to match the flash.
Read more here:
http://strobist.blogspot.com/2008/05/lighting-102-62-gelling-for-tungsten.htmlI find the stofen-type cap is useful in only one place:
I always use it in my softbox to spread the light evenly inside it. Works great there.