Hi,
You don'tneed the NM-HDV2 with the ISR router like the 3845. The PVDM2 will fit directly into the motherboard (up to four modules) and the VWIC or VWIC2 directly into the WIC slots.
This said, if you want 4 x E1 (120 channels) of G.711, you will need 2 x PVDM2-64. If you want compressed voice, like G.729, you will need 4 modules.
Hope this helps, please rate post if it does!