Well, it all depends on the business requirement. Bottom line is that you have to tell the system where to retrieve company numbers from for Revenue and Receivables accounts (and for other accounts too freight etc).

One way would be that we create separate transaction types for each company. This would be a good solution if both companies 1 and 2 sell similar items. We can setup auto accounting to grab balancing segment value from transaction types.

Another way would be that we create separate memo lines for each company. If company 1 sells items 1 and 2 and company 2 sells items 3 and 4 then this would be more applicable. We can setup auto accounting to grab company numbers from memo lines.

On a side note, auto accounting rule for balancing segment should be pretty much the same for all types of accounts (receivables, revenue etc), otherwise you might end up with a journal which is not balanced by balancing segment.

Complex requirements could be handled by SLA where you can override any segment including company.