Like Nihil said 56k is 56.6kbps = 7,075 kBps ... ofcourse this is only theoretical max speed.
Don't forget parity bits, errors, retransmitions etc.

In my contry we use only two wires, and I have the same thing when starting download over dial-up. It doesn't matter if I use IE or DAP.
Here is my theory:
when you start download, while you point to folder where it is going to be saved, download engine (or whatever it is) is buffering that file somewhere in RAM or TEMP file. When you click on SAVE that buffered data is transfered to it final destination, and you have high speed displayed. After that you have the real speed displayed. Actualy I guess that this speed is calculated with difference in file size measured after predefined time interval.

In DAP, when you click on SUSPEND, download is not stoped. It uses extra bandwith (that is not used for browsing at that moment, for example) to buffer data. When you resume, the same thing happens, you have large data flow to file on disk from some temoprary storage/buffer (probably RAM) and high speed calculated. I think this is only marketing trick.

I use download managers only because dial-up has tendency to brake connection, so I can resume download. Or if I'm geting large (101MB for example) file, I can do it for several nights. there is no speed increase.

56k is 56k.... everything you see above 6kBps is only illusion