Can I put other F5 ASM module in different physical box?

Yes, you can use a different BIG-IP box as an ASM-only device, provided that you have an ASM license for your separate device.

It is actually an F5-recommended architecture for ASM scalability when you load-balance several ASM devices using an LTM.

F5 has released a Deployment Guide describing this architecture: Configuring the BIG-IP LTM with multiple BIG-IPASM devices

You can view the deployment guide PDF here:

https://www.f5.com/pdf/deployment-guides/big-ip-ltm-asm-dg.pdf

Hope this helps,

Sam