Nothing at all wrong with using dry yeast for those imperials, 05 for the IIPA and 04 for the stout.
Put enough rehydrated packets on them and you're good to go. Your other option is to brew a lower gravity beer using the same yeast, then either toss the high gravity wort on a portion of the existing cake or harvest a part of the cake and pitch that in a new bucket. If you do either, you have to aerate your wort just like with liquid yeast.
Good Temp Control -----> Happy Yeast ------> Tasty Brew