"Average sized living room"? That doesn't really help

Bear in mind that placing monitors with their backs to a wall will enhance the bass a bit, then consider how much bass you really need. And on the power front, either will be loud enough for you to hear the music through your flat / house.

I'm sure some people will disagree but I don't think a sub is necessary. I personally think either the 624 or 824 will enable you to write well balanced tracks, once you know how they respond. And that's the most important point - know your monitors.

At the end of the day people can compensate for how their monitors respond (or don't respond) by knowing about the deficiencies. Always play stuff you've written on as many different systems as possible and you will begin to understand what sound you need to achieve on your system to make a track sound balanced across a range of systems.

Well, that's a bit OT, so to answer your question, either