It really depends on what you have already. The solutions are almost limitless as far as choices go. You already have a very good streaming solution in the Mac and iPod. As has been suggested, an Airport Express or ATV would be the hub for wireless streaming and also give you access to other music and video services.
Given your budget and depending on your preferred type of set up (lots of boxes vs few), I'd first focus on speakers and TT.
Spend the minimum to get a respectable TT, allocate up to £100 for the ATV/AEX and the rest on the speakers. You could maximise budget by buying used through various used hifi dealers, or even auction sites, as long as you can try before buying. Depends on how confident you are with the likes of the bay though.
Your existing amp may well be fine for the interim, until you can save for a better model, if needed. At least you already have an amp.
I wouldn't say that the DACmagic is overkill, but it will eat up a large portion of your budget for not so much gain, compared to spending the extra on speakers. Speakers will give you the mose diversity in quality of sound presentation and I would give these budget priority, once other needs are met to the minimum.