In my opinion, due to the physical appearance of pmp4000 and pmp3000 look the same, it will most likely also have a common circuit and parts list (at least, most).
Usually Behringer (and all the manufacturers), with the same series / sequence, using the same circuit, the difference is the number of channels only. You can compare the parts list on PMP3000 schematic, with your PMP4000.
PMP4000.

PMP3000


You can download from this link.
http://elektrotanya.com/behringer_pmp3000_sch.rar/download.html
Hope this helps.
Regards.

If the transistors you seek are T2 and T3, they are the power mosfet's and the part number is IRFP32N50K for both. As far as the schematic is concerned, the PMP4000 is a very hard one to find, if you can at all. However, the PMP6000 has a very similar set up and the switching power supply boards are exactly the same board. SMPSU29 is the board in both. The PMP6000 schematic is very easy to find online and as far as I know, the PMP3000 schematic is not as comparable as the PMP6000 is to the PMP4000.