cisco PIX VPN tunnel config problem

I'm having a problem configuring a couple of cisco PIX 501
units to provide a VPN tunnel between the office and a 
branch location.

I can make the tunnel and I can get as far as forcing all 
traffic at the branch down the tunnel and not try to NAT 
anything directly out the branch's ADSL line.

The problem is the PIX at the office end. I want the traffic
from the branch that uses private IP addresses and that emerges 
out of the tunnel to go through a masquerading firewall
so that I can better analyse/filter the traffic and NAT
it back to a public IP address. The problem is therefore
that I need the office PIX's inside interface to send all
traffic that is not to/from the branch's private IP address
network to the masquerading firewall inside the office. This 
means I need the default route to be defined on the inside 
interface of the office PIX and just define a single static 
route for the outside interface to define all traffic to the 
VPN peer IP address to go through the office outside router.
ie,:
  route inside 0 0 10.12.0.1
  route outside 213.16.240.80 255.255.255.255 163.1.63.254

The office PIX appears to accept these commands but then
the VPN tunnel doesnt work.

Reverting to:
  route outside 0 0 163.1.63.254
  route inside 163.1.63.0 255.255.255.0 10.12.0.1

does work - the VPN tunnel works - but then remote machines
at the other end of the tunnel can only get to office machines
ie, in 163.1.63
It would be rather tiresome to have to define static routes
for the whole of the internet subnet by subnet!

What i just dont get is why the tunnel doesnt work with
  route outside 213.16.240.80 255.255.255.255 163.1.63.254
where 213.16.240.80 is the IP address of the PIX at the
other end:
  crypto map branch 10 set peer 213.16.240.80
  isakmp key ******** address 213.16.240.80 netmask 255.255.255.255

I have also tried:
  route outside 213.16.240.0 255.255.255.0 163.1.63.254
but that doesnt work with the VPN tunnel either.

The PIX is running 6.2 (see detailed config below) but I know
that 6.3 is out. I dont know if this "firmware" upgrade would help. 

If anyone knows why I cant make a VPN tunnel with a default route
on the inside and a single route to the VPN peer on the outside
interface then please let me know. I would be very appreciative.

Many thanks,

Sincerely,

A. Johnson

----------------------------------------------------------------
Cisco PIX Firewall Version 6.2(2)
Cisco PIX Device Manager Version 2.0(2)

Compiled on Fri 07-Jun-02 17:49 by morlee

officepix up 6 hours 30 mins

Hardware:   PIX-501, 16 MB RAM, CPU Am5x86 133 MHz
Flash E28F640J3 @ 0x3000000, 8MB
BIOS Flash E28F640J3 @ 0xfffd8000, 128KB

0: ethernet0: address is 000b.be57.63ef, irq 9
1: ethernet1: address is 000b.be57.63f0, irq 10
Licensed Features:
Failover:           Disabled
VPN-DES:            Enabled
VPN-3DES:           Enabled
Maximum Interfaces: 2
Cut-through Proxy:  Enabled
Guards:             Enabled
URL-filtering:      Enabled
Inside Hosts:       10
Throughput:         Limited
IKE peers:          5

Serial Number: 806505814 (0x30124d56)
Running Activation Key: 0x56dd0701 0xa800be04 0xc2bcc8d0 0xf6e11654
Configuration last modified by enable_15 at 16:33:25.310 UTC Mon Dec 1 2003

------------------ show config (run time) ------------------

:
PIX Version 6.2(2)
nameif ethernet0 outside security0
nameif ethernet1 inside security100