Anybody know if this will work?
Tascam PS3500
I'm assuming this mates with an M3500 console...it looks like the same connector but
no umbilical.
Ethan and Somnium7, thank you both for the offers, and the encouragement. I will definitely keep that in mind. I'm likely to hold out a bit longer for a PS520, but if push comes to shove I will definitely look to build one with some help from my friends! 
This M520 is, in my experience, a pretty unique package. I've read, in depth, the manual up through the functional description of all the features including the block diagrams and such.
I realize that some of the relatively unique features are precisely those for which the M500 consoles (and others) have drawn criticism, but I think its cool!
As I've said in the past, I have quite a bit of experience with an Allen & Heath GL3300-32, from operating to training and even modifying the innards. I have also owned a couple small mixers of no fame, and in my research over the years as a gearhead I've read the manuals to probably 40-50 different consoles. I like learning how different vintages, makes and formats of mixers go about accomplishing their tasks. My reading has covered both analog and digital consoles and I also have quite a bit of experience operating the Yamaha 01X that perches in my studio.
I have to say, again, the M520 has a number of fairly unique features for the price range especially. What it lacks in +4 balanced outputs it makes up for in routing and patching flexibility and faculties. I can see it is open for criticism with the dominant -10dBu RCA I/O, but I think some of that is the same market hype that I've fallen prey to as well...+4dBm operating level does not necessarily mean better signal quality, and in some cases worse.
The aux section, while limited in only 4 channels by today's standards on a board of this size is really, really flexible...pre/post switchable in pairs, individual send level pots (albeit concentric stacked pots)...nothing too special yet, but then the ability to draw (in pairs) signal from either the channel line or mic input OR the channel tape input with the flick of a switch...now you've got two effects sends and two cue mixes...or flick-flick-flick you've got 4 separate cue mixes, and having aux mute switches on the strip (again in pairs) is a handy feature.
I also like that the line level and mic level inputs to the strip have separate gain trims.
And of course the eq...I can understand some bellyaching about the absence of shelving eq, but, as is usually the case with this vintage of Tascam gear, they have a wonderfully logical way of explaining why they did what they did and offering some education in the process. You can do a lot of bad with shelving eq. Such a tendency to grab the high and low level shelving eq knobs and turn 'em up...in a live situation, depending on your signal path you could be really loading your amps and drivers with mud...I already liked the idea of a three-band sweep eq, but now that I know the method to the madness I like it even better. It offers more flexibility and also forces you to be smart about your eq'ing, the way its supposed to be IMO...
Each channel strip has a crazy amount of patch/access points...including the insert send and return there are a total of 7 jacks per channel on most channels, more on some.
Plus the monitor section can be used as an additional tape cue (again with the flick of some switches) leaving all 4 auxes free with no repatching, or it behaves like an 8 x 2 matrix mixer or anything in between, again, all with no repatching.
They doubled most of the output jacks...with a matching patchbay this thing would be pure madness in terms of flexibility...
And while it doesn't feature dedicated main outs on XLR's, it all depends on how you want to configure things with the balance amp section...8 unbalanced -10 RCA inputs, 8 +4 (or +8) balanced XLR outputs...patch away.
Yeah, there is no way to bypass the subgroups and route straight to the main buss, but really its all in how you want to patch and configure, and it
does have individual buss assign switches. It really is a pretty smart design and I imagine it may have, in part, fallen subject to the consumer demand for a board with 1/4" jacks instead of RCA's...
But wait! There's more! Channel PFL
and solo-in-place circuits, master section talkback and oscillator features add to the package...8 of the 12 VU meters can monitor external sources or
anything you patch to them at the press of a switch in groups of 4...now
that is cool. Again, an appropriately-sized patchbay would just make this thing a flexibility monster.
Individual phantom power, phase reverse and pad...the channel strips don't look very feature packed until you start seeing all the routing/source select switches and then realize that 6 of the 7 pots you see on each strip are stacked...
Plus instrument DI inputs on channels 1 & 2...phono preamps on channels 3 & 4...two stereo returns on channels 17 ~ 20 available in the monitor section at the push of a button...the list goes on...
I'm concerned about burdening you and others with so many questions on specifics, and I don't want to move forward with a parts order and then not have direction to complete assembly. Keep in mind I think my experience/comfort level is quite a bit different than yours...
