Ok you need 4 USB-cable but is there a speed decrease?
Not different. a k64 is just 4 k16, not cut up into 4 boards but kept as 1. They are connected between each board, not by usb but by a ribbon cable. All you will need is one usb cable, and i think you can connect/chain up to 8 boards in one ribbon cable or was it even 16 boards.
I would assume 8 of them, since that is 128 chips (USB hosts can accept 128 devices, and i would assume that the controller on the K16 either follows this rule or applies a similar rule to the chips it controls)
No, the USB protocol is not used when communicating with the chips. Each 16-chip board is shown as a single device when connected via USB. If you use the built-in chaining capability of the boards (which uses the i2c protocol, not USB) it still shows up as a single USB device, regardless of how many boards you have chained together.
okay, thanks for clarifying. On some research, it looks like i2c is limited by the number of pins used. If 3 pins are used, 8 devices are the limit. 4 pins should enable 16 devices. how many are on the K16/K64?