Pros and Cons of built-in amps?

It would seem to me that running the source through a quality balanced cable directly to the speaker would be the way to go if possible.

Yes it is the way to go if you want professional quality fidelity and low distortion. If you prefer a more forgiving or nice sound then you may find it too much of a straight jacket to live with. Each recording sounds completely different (more different then you will have been used to ever hearing)...so you lose some of the flexibility to tailor the sound. Room modes can become more problematic because of low distortion => basically any issues become more noticeable....so it is not without frustrations, bad recordings and distortion that makes it way on to a recording will more easily grab your attention - this can actually spoil some of what may have been long time car stereo favorite tracks...

Pros
Much Lower IMD (each amp drives a separate narrower band and basically has an easy life compared to a regular amp driving a difficult speaker load)
Greater Dynamics/SPL (no lossy crossover, amp tuned to load)
Phase compensated => good impulse response = good on drums/percussion
Less background noise hiss if you use balanced XLR cables and source gear
ATC's use Class A amps up to two-thirds power
Much less chance to ever blow up the speaker drivers(momentary gain reduction is possible in each amp which is specifically designed for each driver)
Low cost - overall since it is easier to design amps that drive an easy load over a narrow bandwidth then you not only get better amplification but it can cost less too.
No need to worry about speaker cables or run lengths

Cons
Nead an AC plug for each speaker
Speakers are even heavier - shipping for resale can be a problem!
Repairs may be more costly if you have to send speakers back to get amp packs refurbished/recapped/calibrated (usually every 15 years or so)
Resale to audiophiles is limited so you may not want to get the "Anniversary" editions with stunning veneers but a black ash box or a pro model instead (active is only popular in pro markets and pros care very little for ultra expensive veneers...)
Troubleshooting - obviously integrated packages are harder to nail down to the root cause.

Listen to this lecture(bear in mind Meridian sell Active Speakers - so take everything said with a grain of salt)

Do yourself a big favor and find a PMC dealer. Then listen to a pair of properly broken in AML-1's with music with which you are familiar. I replaced Avalon Eidolons with these and, as fine as the Eidolons are, I would never consider anything other than transmission line bass with active dedicated electronics and no speaker cables.

Yes these PMC's should be on your audition list - I would add the Genelec 8050A's too - a real bargain when you consider what you are getting for around $4500 new - I am impressed with their bass response - so much so that I could not believe that these small speakers were actually ported! Overall a very nice balanced articulate presentation (you can easily hear every detail in the recording but it is not torn apart as some studio gear is known to do). They also image like there is no tomorrow. The metal dome is not to my taste but many people love the clean crisp sound!

Try ATC 19s or 20s--really great speakers for the money--slay all the competitors in their price range. Like all British products, you will be hampered by the low dollar to Euro.