We also faced this scenario, what I can understand from you is, you need to maintain a relationship of Sub Asset with Main Asset.
We have the following option available: -
User Structure Fast Tab in Fixed Asset Master
Open the Sub Asset "Engine"
Go to Structure Fast Tab and Assign the Main Fixed Asset in the Main Fixed Asset Drop Down.
Now in the Fixed Asset List Page you can insert the Main Fixed Asset Column to check the relationship.
In this way you can assign multiple assets to main asset, and you can filter on the Fixed Asset List page using the main fixed asset number.
If there is any other thing that you asking let me know
