net module write sending string only

Yes, socket.write expects a string (or does a simple toString on whatever data type you give it). The simplest way around it is to use E.toString(...), for instance:

>E.toString([0,1,2,3,4])
="\x00\x01\x02\x03\x04"

If you did socket.write(E.toString([0,1,2,3,4])) you'd send just the 5 bytes 0..4.

You could use String.fromCharCode(...) which is standard JS, but E.toString is a bit easier and more efficient when dealing with arrays.

Sending floats is a bit more tricky, but you have 2 main options:

Typed Arrays

var a = new Float32Array(1); // one element array
a[0]=564654.24245
xyz.write(E.toString(a.buffer))

DataView

This got added as of 1v92, and it lets you store and read all kinds of data really conveniently:

http://www.espruino.com/Reference#DataView

var d = new DataView(new ArrayBuffer(8)); // 8 byte array buffer
d.setFloat32(0/*byte offset*/, 765.3532564);
d.setInt8(4, 42); 
// etc..
xyz.write(E.toString(d.buffer))