Hello Ali,
use an LACP negotiated bundle instead if both member links go the same switch or if the two swiitches can appear as a single entity ( C6500 VSS or C3750 stack are examples between cisco products other vendors may have similar virtual chassis solution).
if the lan switches are two different entities you cannot use LACP to negotiate over the bundle-
if this is the case you can consider to split the broadcast domain/ip subnets in two parts in order to use two indipendent L3 interfaces on the ASR 1006.
feature navigator can be of help in finding a newer IOS XE image that supports IRB
http://www.cisco.com/go/fn
search by platform
I tried both ASR 1000 RP1 and ASR 1000 RP2 processors but as far as I could see IRB is not listed
Hope to help
Giuseppe