Based on your requirements, I put together the following parts for the central tower system only.
Good solid motherboard; quad core processor for multi-tasking and CPU-intensive software applications; Excellent and quiet CPU cooling; the Case is a subjective thing, it's one's own taste of course, but the suggested case is quality; quiet 500W PSU; Best DVDRW for the money plus a DVD drive for playback only & copying from; Two hard disks (Samsung are very quiet), the smaller one for all your software and Operating System, the larger one for storage; The Matrox graphics card is perfect for your work applications and supports a three monitor display, but is a bit rubbish for gaming; Superb sound card for audio work; and 4Gb of fast memory.
The total price inc VAT & postage is £1059.64
Which leaves you £440.00 for three monitors, keyboard, mouse and speakers, which, frankly, you ain't gonna do.
I think for your needs a £2K budget is more realistic.
However, corners can be cut, but I would strongly suggest, in view of your needs, you do at least stick to a quad core CPU; The Matrox Graphics card and the Creative Sound card.