Music business giant EMI has agreed to be bought for a cool $6.3 billion by Terra Firma. But after Microsoft’s [unrelated] $6B acquisition last week, who can keep track?

That’s like buying 10 Mona Lisas. (Probably seven, once you adjust for hedge fund dollars and inflation since 2005, when its value became wikiable.)

EMI made waves last week when it announced a deal with Amazon to enable an online mega-store to rival iTunes. (Nice to see that Rolling Stone & ZDNet agree with us.)

Back in April, Read/Write Web rightly wrote about Apple’s “stranglehold…over the online/digital music market.” But things have changed.

In the tech world, such mega-acquisitions have inspired shock, awe, and shades of WTF? But this deal might have an equal and opposite reaction from the business digerati because it’s enabling competition among giants.

At the end of the day, though, Amazon, not iTunes, will be selling Beatles tunes. And, as they say, ya “can’t buy me love” (for under $6.3B). Still, it’s comforting to see this much being paid for a company that just owns, ya know… content. With a little help from their friends over at Amazon and iTunes, EMI is poised to play all sides of the very same digital music biz that it seems they’ve just improved.

Terra Firma, indeed.