Trouble with a tripel

I feel like I have bitten off more than I can chew here so I am looking for some advice. I currently have a recipe from Sam Calgione's book Extreme Brewing in primary fermentation. My first mistake was using a 5 gallon carboy for such a high gravity beer. According to the recipe, I am supposed to add some brown sugar today or ASAP. Last night, I had some krausen in the airlock so I removed it (and cleaned up an explosive mess in the process) and opted for a blowoff tube, which has helped.

My question is, do any of you see a problem with just taking off the bung, and throwing it all into a primary bucket that is 6.5 gallons when I add the brown sugar? I am afraid that I am going to have the same problem after I add the sugar. This will obviously give me more room for extra krausen and hopefully control things a bit more.

First off, there is nothing wrong with transferring to a bigger bucket. However, there is a big problem if you plan on just "dumping" the beer in. That would produce an immense amount of oxygenation. Do you have a an autosiphon or racking cane?

6.5 gallons is big enough for pretty much any 5 gallon batch. In the worst case, you setup a blow-off tube.

I can absolutely rack it over...do I need to get everything or will the trub on the bottom be better left where it is?

How far are you into primary fermentation? If you're only a day, two days, or possibly three I would have no issues with carefully racking into a bucket. If you're further along I think you'd lose some yeast mass in the bottom of the carboy and I'm not entirely sure it would finish properly. In that case I would just add the sugar to the carboy and leave the blowoff in place.

As you are finiding out, a lot of the true Belgian yeasts are robust top croppers. WY3787 foams until theres no tomorrow. Adding Fermcap S will reduce some of the foaming (an option for you), but it will not stop it.

I brewed this on Sunday so we are 2 days in. Do I take everything I can to the bucket?

I ended up leaving the batch in the primary instead of racking it and attaching a blowoff tube that is 5/8" instead of 3/8", just in case the krausen builds back up after adding the brown sugar. The yeast is still doing its thing, so I'm going to cross my fingers and hope for the best. Thanks for the suggestions and help everyone. Cheers!