Hi Gareth,
Definitely check out the DirectOut stuff. They are designed by Stephan Flock, the guy who did a lot of work for RME in regards to their Madi gear. DirectOut have a bunch of MADI options, most with redundant PSUs. They also allow you to configure the MADI ports to your needs (optical/coaxial) and some models also include sample rate correction if required. Pricey but great from all reports. Built for pro and broadcast use. See this link
http://www.directout.eu/en/products/andiamo.xt-src.htmlDirectOut also supply madi cards that fit into existing RME Madi gear (such as the Micstacy and ADI8QS) to extend the limited routing options. The routing matrix made available on these retrofit cards (as opposed to the RME variety) allows for free routing between the ADAT, AES, & MADI i/o on the ADI8QS for instance.
The other obvious MADI choice is the SSL Alpha-link range (which are meant to be great bang for the buck. I have not heard them so cannot really comment on their audio performance). I have heard negative reports about setting them up however, as they are apparently not the most intuitive when it comes to their user interface, especially when trying to route elements to a madi stream. The Alpha-links also allow you to add in AES or ADAT interfaces on top of their analogue i/o, depending on which Alpha-Link model you choose.
I picked up a cheap Euphonix AM713 (basically the standalone S5 converter) which is great but hard to find standalone, especially here in Australia. These are only MADI to analogue, or analogue to MADI in a separate 3-RU chassis. Built like tanks, with 28 inputs or outputs (including two auxiliary digital i/o).
The Lynx Auroras also have a MADI card available (about US$650) which also has an advanced routing mode if required (much like the ProTools card). In this mode the Lynx gives you access to all 32 ins and outs simultaneously. (16 analog i/o and 16 AES i/o all at once). This is a great option all within the one rack space. Latency is also very good on these Auroras.
Mytek also have a MADI DIO card (which fits into one of the two DIO slots on the back of the their 8-channel 8x192 converter). These can be cascaded if you need more than eight channels. You set up which bank of 8 channels to insert into the MADI stream, via the DIP switches on the DIO card.
Hope this info helps.
Cheers,
George