Take the sponges from your Aquaclear's and just drop them into your overflow. I've done this many times and it works great. That way you don't have to look at those ugly HOB's with a nice 125g and sump
Thje sponges will float on the top of the water and get good airation wich speeds up the development of bacteria. As the water falls from the overflow to your sump, it takes that bacteria with it and deposits it on the bio balls. Like I said, it's worked for me in the past.
Also. With that bio load "I" wouldn't be too worried. If you can I would add all the water from your 38 to the 125. Drop the sponges in the overflow and add the fish. Of course keep an eye on the ammonia and nitrites, but that is not that much of a bio load for that size of a tank.
Also, feed lightly for about the first week.