How to "translate" Grep search / replace commands working with TextWrangler using the command line

I have Grep search / replace commands working well under TextWrangler , as shown below:

Find: (\ "\ d +. \ D {3}) + (\ d {3} + [\ s] +)

Replace: \ 1s

For example, this find / replace will replace:

TXTXTXT "123.123456 TXTXTXT from TXTXTXT" 123.123sTXTXTXT

Now I want to do the same on the command line using egrep, but it does not work:

egrep -e 's/(\"\d+\.\d{3})+(\d{3}+[\s]+)/\1s' -f m.txt > n.txt

egrep: regex too large

Any idea? Thank you in advance.