Hi RCG,
Sage BusinessWorks only allows one sales rep per invoice. The commission is based on the invoice, not by line item. You can send enhancement suggestions to [email protected].
Thank you,
Janice

Since my company is shopping for new ERP application, I will chime in on this too.

Sage 200 and X3 have the ability to split commissions

We have also looked at these :
Deskera
Exact Macola 10.4
NetSuite
Kenandy

If BW is on your radar, look at the user requests for changes (over the years) and then look at the current version to see what changes have or have not been added.

We currently dump all BW invoice line items and hand code the split commissions ( since 2003 )