Hi Peter,
1) Does balanced cables mean that the two are balanced to each other, ie cut form the same length, or something akin to that?
Nothing like that, I'm not an electircal engineer by any stretch but I believe they use a differnenet design topology. RCA cables are unbalanced and XLR tend to be balanced, although this isn't always the case for example if you use RCA to XLR cables. There shouldn't be any differnenece in qulaity although some report instances where there is. Balanaced have an advantage in that they are better at rejecting noise which isn't an issue in a domestic set up anyway, musicians favour them as they have long cables and often crossing one another on stage etc. Balanaced sometimes operate a little louder which can give the impression they sound better or also can be useful if the extra gain is needed.
2) Will that matter if I only need two half metre cables? Once the cables are installed they will probably only ever be disconnected during upgrades/decorating, so they don't have to have a microphone quality build.
It shouldn't matter. Short is best at any rate.
3) Will my system of Audiolab M-DAC / M-PWR sound any better than with XLR cables than the Chord Chameleon RCA's I currently use. The one review I saw of the M-PWR said that XLR's made a difference but if anybody else out there has experience, please let me know.
Hard to say, I doubt it but it may be louder. Still I use XLR out from my M-DAC, I just like the way they fit if nothing else!
4) What sort of budget should I be plumping for? My head said £150, so the cables talked about in this chain are coming in considerably less
Don't throw that sort of money on XLR cables. Get something well made but with no bling, pro audio shops for about £50 will be perfectly fine..