While looking for information on a Boca modem that contained a Cirrus Logic chipset (CL_MD34xx), I found a good AT command reference manual for this chipset at:
http://www.logicode.com/download/cir33txt.exe - which is a command reference manual for a Logicode modem with the same Cirrus Logic Chipset.

After many connection failures (even with speeds as low as 14,400), a technician from Boca said that downloading:
ftp://ftp.bocaresearch.com/Drivers&Software/File_area_14/ - The file needed is called 4385dos.zip

I have not verified that this resolved the issue, but I have not yet heard back from the customer - which is usually a good sign!

Well as you can see We are looking HARD for the init strings for the cirrus logic.
We do believe we have found the one that works ok on terminal servers hence dialup routers:

atm1l3&c1&d3&k3&s0=1&w
the one for echo off would be as such:

atm1l3e0q1&c1&d3&k3&s0=1&w

Cirrus Logic makes chipsets, not actual modems.

If you cannot figure out who made your modem, CLICK HERE for information concerning the FCC ID lookup tool