[Darryl Ramm]

And a pack of chewing gum would be cheaper as well and about as relevant. :-(

You really should be thinking about the total system configuration and what you need. If you are going to all the trouble of mixing in an analog console and not ITB I would hope you have a fairly high-end $$ console and the analog interface costs to go with that would often not be a huge issue.

Again the basic limits that you need to worry about have not changed in a long time:

For more than 32x32 IO you need Pro Tools Ultimate with a DigiLink interfaces

You cannot combine via software or aggregate DigiLink interfaces with non-DigiLink interfaces.

You can connect outboard interfaces/preamps via ADAT/SMUX, S/PDIF, AES/EBU etc. to a DigiLink inerface.

If you need more than 32x32 input or output you are stuck in DigiLink land. Choices are Avid's 96 IO, 192 IO, HD IO or upgrading to a new much more $$$ MTRX, or adding more Symphony cards or chassis, or other third party DigiLink interfaces. I'd try very much to stick to all one interface vendor, including for identical latency and ease of configuration.

Is your Symphony maxed out with two 16x16 analog cards? Is it an original or Mk II? I'd hope you could pick up a 16x16 card used or just buy another Symphony chassis with cards in it. I see occasional first gen used boxes for sale more than used Mk II.

Also not clear how many HD TDM cards you have, remember 32 IO max on a single DigiLink TDM card port. Do you have enough TDM voices and DSP to deal with all these extra tracks and mixing OTB?

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I'm guessing you really want to keep the TDM system for low-latency tracking. If that was not a factor and this was mine I'd probably try to get to a more modern system and be getting off HD/TDM and onto Native and mixing ITB with the 64 float mixer, maybe saving money by selling off HD/Ultimate and selling some of the gear. Possibly saving up money for control surfaces.