The above reply is good - but I wouldn't reduce most instruments to totally mono that's just me I think the stereo information is important in there. IF you are going to mono them, I recommend muting one channel instead of using powerpan because you are blending the two channels together, a more accurate representation of a mono recording of the instrument is to simply mute one channel as though it was only recorded with one mic to start with. Since they were recorded quite close together, that makes sense to me. Second to that, from what I have seen so far - get MIR PRO! It will solve all those problems and in a fast and easy to use efficient interface. VSL library was designed to be used with something like MIR Pro in the future (which is now) - all instruments recorded at I think the same distance, on a specially built dry stage. This allows maximum flexibility later on, but of course with flexibility comes more work to be done - they're not ready out of the box. But MIR seems to solve all of that perfectly - you get the flexibility and ease of use at the same time.
For bass reduction I have dropped as much as 12db off certain instruments to help place them up to as high as 1khz. They are recorded in all their full glory in this library, so you have to do that to place things. Listen to the same instruments in recordings you like and listen to their freq distribution.