Ok a bit cheeky but i'm hoping there's some home cinema buffs on here, i'm thinking about getting a sub, i've got a pair of floor standers - Monitor Audio Silver RS5 with a Denon AV2311 receiver, would be grateful for any advice or opinions, how much to spend etc.
REL is always a safe bet - depends on how much room you have.
Look for RELs that hold their value 2nd hand - pick one up off ebay or similair and try it. If it doesn't work in your room you can sell without losing too much.
Get a no-name cheapo and you wouldn't get much back on it.
Look for a steep upper crossover slope at 100hz - any higher and you will be able to place where it is. The steepness of the curve will aid its integration with the rest of your system.
i think the monitor audio sub matches them quite nicely?
i've got BR6 setup and I'm unsure as to whether a sub would really help out (as its already got 6x6.5" cones) - but on a set of speakers like yours itd probably be really beneficial