Anybody know the significant differences between the C1 and A1 besides the fact that there's a Beachtek-like box on top of the A1?

Actually it's a PDX10-like box. DV vs. DVCAM is the other big difference.

I'm not following you. How's a PDX-10-like box different from a Beachtek? And regarding DVCAM vs. DV, doesn't that basically mean shorter tape-shooting times (40 vs. 60 min.)?

The major advantage of DVCAM over DV is the signal is recorded at a lower 'density' (if that makes sense) so it is more resistant to dropouts. It is the same signal as far as audio format and video resolution/compression is concerned. It also supports locked audio. The consumer dv format also supports this, but in practice they are always (?) unlocked.

I would think the box-on-top would have internal circuitry very similar to a beachtek. Haven't seen inside one (or a pdx-10) though.

I don't know how the PDX-10 box compares to the more expensive beachteks, but I have a DXA4 for my VX-2000. It is fine, but the PDX-10 box seems a little more refined with more options for choosing input, mike attenuation, low cut filter, and it has phantom power. Basically, it's a removable version of the PD-150/170 XLR box. The Beachtek box is also a lot larger and much heavier.

More importantly, the PDX-10 box connects through a multi-pin plug that snaps into the intelligent hotshoe so you don't need to go through an 1/8" miniplug input like a Beachtek does. This plug provides phantom power and also tells the camera the box is present, which affects your menu choices. I assume it also provides a cleaner preamp input, but I really don't know that for sure. However 1/8" mini-plugs don't have a very good reliability record, so I think the hotshoe approach is an improvement.

I don't have any experience with the PDX-10's cousin, the TRV-950, but I can say that PDX-10 audio is much better than my VX-2000.