For channel banks I would search for adit 600's on ebay, Dell used to sell them, they are cheap as sh*t and are extraordinarily configurable and the FXS cards are at bargain basement prices because Dell/m$oft no longer support them (adit do ), the REALLY useful, FXO cards are hard to find but work as well as anything for a couple of hundred bucks or less for each 8.
They are 19 inch rack-able but the ears and connective hardware (two Adits x6 FXS's for 96 channels in 2U) are hard to find, so use shelves. So you would need 6xAdits and thusly 6U rack space bujt you get some spare pairs, each one has two RJX-25 for legacy 66 block wiring. and a 48v DC power option
(I know all this because I have been using them for years. Not so much anymore, so I have/am trying to, sell them to the cognoscenti)