i think there is a little confusion here?

there are 2 terms:
KB/s (kilobytes per second) mostly expressing the 'transfer volumes" (1KB = 1024 bytes) thats what xolox says

kb or kbpps (kilobits per second) expressing the 'streaming speed" (thats what the modem says) (1kbps = 1000 bits)

there are 8 bits in 1 byte, and 1024 bytes = 1KB

So when the modem says 56Kbps... you could (in theory) have a volume download of :

56000 /8 = 7000 --> 7000 / 1024 = 6.8KB/sec

But the "quality and speed" of a modem-connection has limitations... so if you are getting 3 to 4 KB/s with a 56K modem... be happy!

(thays why users do get a "download accelerator or a "tweaker" who (sometimes) "boost" the connection up to 7, even 12KB/sec.... but is it always compatible.....

In Xolox, set your "max upload speed" to 2KB, othherwise Xolox will "eat" all the bandwith that is left (if there is)... and your browsing could become veryyyy slowww