When you say that you just purchased it, how long ago are you talking? My S7i has plenty of bass slam, drive and fullness.
Remember two things. The unit has to break in which takes a few weeks. Once it's broken in, if you turn it off, once you turn it back on it takes hours and hours for it to achieve it's optimum thermal operating temperature.
If it's broken in and you're leaving it on all of the time and you're not getting what you want from it, you may want to look into upgrading your amp.
If you're running the S7i in the 75-100 range, you're right where you need to be. But when I first bought mine, my Karan KAI-180 couldn't keep up with it. I bought a Burmester 036 and it couldn't keep up. I bought a Pass XA 30.5 that could, but it wasn't powerful enough for my speakers. I bought a Spectron Musician III Mk2 that serves it really well.
The S7i throws out an unbelievable amount of music that a lot of amps can't process fast enough. I imagine that the new bigger Bryston amps might be alright, but I've read that the older ones can't really touch the newer ones capabilties.
Just relax, you've got one of the best digital players out there. Enjoy it as it is for now, and when you have the time and money, start experimenting with your amp if you want. If you like your Bryston, look at the newest and bigger ones, or Pass, Plinius, Spectron or BAT. I'm sure that there's other brands too, you just probably need their top of the line amps.