[c-nsp] Cisco NMs for DS3, equivalent to Adtran MX2800 mux-er?!?

[Network Fortius]

Given:
DS3 on a Sonet ring, coming into the building into an Adtran MX2800  
(http://www.adtran.com/static/ENTERPRISEPRODUCTS/T3/MX2800UNITS/ 
1200290L1.htm), with T1s from various locations mux-ed together by  
our ring provider. The Adtran device then splits them into separate  
T1s (some "pure" data, some voice and data), and delivers them to  
individual CSU/DSU units, which then split voice and data into PBX  
and serial interfaces of a router, respectively, or - the pure data  
T1s - straight into serial interfaces of the same (old Nortel)  
router. In an attempt to replace this router with a Cisco 3845 (as  
previously - and correctly - recommended by someone on this list,  
earlier), I ran into a problem in the design phase: if keeping the  
existing setup with Adtran, and just trying to replace the Nortel and  
the CSU/DSUs, I would max out the 3845 because of the need for VWICs  
and VWIC-DI cards.

Question:
Based on the above info - my thought is to try - next - to replace  
more of the upstream devices, such that I would not get individual  
T1s (data, or voice&data) with their corresponding VWIC or VWIC-DI  
cards, but rather a whole NM with a DS3 interface, then do the demux- 
ing in the Cisco, vs. the Adtran (the idea being that all these  
routers - old, as well as new - are nothing else than "consolidators"  
of remote WAN lines into one single ethernet interface, with  
appropriate routing at the IP layer, for each location). Does anybody  
know of a way to address something like this, and/or parts I should  
read more about?

TIA,
Stef