I don't know much about the sound side of computers, so I'll leave that to the others to discuss.
You can build a desktop/tower capable of running mac os and windows/linux rather than buying an apple pc, it's cheaper, future proofed etc.
Depending on your budget, it would work out something like
Case - I like lian li cases, but there's tons to choose from
Mobo - I'll leave this blank, as an audio rig there may be a preference. Choose a mobo wisely, I personally think it's the most important component.
Processor - I5 is a great entry level, there's not a huge difference between it and the I7, go for unlocked core (denoted by a 'k' at the end of the model) to open up over clocking.
Heat sink - (If you don't intend to over clock, or only marginally, then the stock that comes with the CPU is sufficient)
Ram - 100 6gb minimum, I'd recommend 16gb, I love corsair vengeance ram. Graphics apps make full use of RAM, I assume audio apps would be the same
SDD - For the os, so doesn't need to be huge.
HDD 1 - For use as a scratch disk, again doesn't need to be huge.
HDD 2 - Storage, 7200rpm is good, I usually use green drives for storage
HDD x - As many hard drives as you need, obviously bumps up the cost. RAID array's aren't necessary for most people. Utilise cloud storage for redundancy.
PSU - 650w is sufficient for most rigs.
Graphics card - I don't really know what's new in the last year or two, so leave this for someone else. I use a radeon 6870 (I think), my rigs 2 years old.
Fans - Stock fans are usually fine, you can upgrade for sound efficiency, or extra air flow if needed.
I currently run windows 7 and mavericks in dual boot.
From my mac overview
Code:
Model Name: iMac
Model Identifier: iMac12,2
Processor Name: Intel Core i7
Processor Speed: 4.41 GHz
Number of Processors: 1
Total Number of Cores: 4
L2 Cache (per Core): 256 KB
L3 Cache: 8 MB
Memory: 16 GB
This cost me about £1000 2.5 years ago, the same rig today I reckon could probably be done for 600-700. The same rig as an apple machine, probably still £3.5k+
If you want to put parts together, this is a good tool
http://uk.pcpartpicker.com/
Android should make an OS ( unless I'm mistaken and they already do?) and create a new system.
They make Chrome OS, it's geared for netbooks and utilises the cloud. Never tried it though.