Regarding Bus Powered interfaces and other things.
 
A computer USB (or firewire) bus can only deliver a certain amount of current. Current is what matters, not voltage. Although the 2 are closely related in the ohms law formula. But ultimately, the amount of current that a bus can deliver has to be divided between ALL of the other things accessing that bus. If I understand correctly, a single USB port is limited to less than the total available current the bus will provide.
 
It's generally not recommended (by some manufacturers)  to rely on bus power for interfaces, unless you have experimented and find it to work satisfactorily and are in a situation where it is necessary to rely on bus power. If you have an external power supply for the interface, use it, since it IS designed to run the interface properly and within spec.
 
I have a Focusrite Saffire Firewire Interface. It came with a wall wart power supply and on a laptop it is imperative that the wall wart be used since the laptop only has 4 pins and not 6 on the firewire ports. On my current desk top, I can run it from the FW port since it has the 6 pins but I still have it plugged into the wall wart as well. It runs fine with both.
 
I have another program which came pre-installed on a SS-HD and it is USB bus powered. There was NO wall wart in the box. However the instructions say to use the USB connector, which has 2 USB plugs on the computer's end.... and to use BOTH plugs connected to 2 ports on the computer if one doesn't provide sufficient power. Apparently, USB ports are limited to a certain amount of current each but paralleling them lets you double the available current if needed to run the drive.
 
Focusrite interfaces have really nice, transparent pre's. they should not be adding an inordinate amount of color to the sounds going through them. If they are, you need to check a few things. Be sure the Focusrite control panel is set up properly. Mine has compression, EQ, and reverb available as well as controlling the gain settings and output volume.