It's a bit sad to admit but I know tons about soundproofing. I'm a musician and used to own a rehearsal and recording studio. Aside from the ceiling, our biggest bleed was through the doors.
You will need to bear in mind fire regs if you are changing your doors. Fire doors are great but by nature they are very heavy and you may need to make other adjustments. Another alternative is double doors but if you have a floating ceiling this is pointless. We lined our doors with rubber matting that was slightly bigger then the doors so there was an overlap. This worked really well but looks very utilitarian.
Re ceilings and walls it really depends on what sort of noise you want to block out as sound waves travel different distances depending on their frequency.
HD65 is a soundproofing foam that is quite good at holding back lower frequency noise and acoustic foam (with a huge surface area because it looks like egg boxes) is better at holding back a treble frequency.
Above the ceilings in the studios we used a layer of high density acoustic plasterboard, then a layer of HD65. On adjoining walls (ie between two studios) we had stud partitions. These were lined each with a layer of high density acoustic plasterboard, then HD45 then a layer of lead-lined foam then acoustic foam to finish. The result from an acoustic point of view was AMAZING, a really crisp clean sound where every nuance of a played note was audible. From a financial point of view, it was a nightmare. The foam is very very expensive, think also of the adhesive - has to be very strong (especially for the lead lining) and the man hours to install.
I'm not sure that's been much help really....can you move premises or just turn up the piped music?
take a look here for more info
http://www.soundservice.co.uk/articles_index.html
