There's almost certainly going to need to be two models to do this neatly. Assuming the fields in Excel are Payee, Date, Amount, and Payer, then a Summary in Monarch with Payee as one key, then another key of Payer which you can set to hidden (this will group the payments that match together), then Date as a key set to display Across rather than down, and Sum(Amount) as a measure. This will get you some of the way there, but you'll probably want another pass through Monarch to clean up the white space.
Based on the input file information, I created a test spreadsheet with the following data:
After opening it in Monarch as a database, I created an external join that points back to itself and joined on the Employee[/B] and Payer[/B] columns. Monarch will detect this does not give a distinct listing and will ask if you want to use the first value it comes to for the other columns; in which, the answer is "Yes."
Afterwards, I created a filter using the following expression:
Since an employee shouldn't get paid the exact same amount on the exact same date, this, in theory, should give you the result you're looking for.
Employee PayDate PayAmt Payor
Aaaaa Aaaaa 2011-02-13 1025.22 Company ABC
Aaaaa Aaaaa 2011-03-12 1050.31 Company DEF
Bbbbb Bbbbb 2011-02-03 957.12 Company GHI
Bbbbb Bbbbb 2011-02-18 985.60 Company ABC
Cccc Cccc 2011-03-01 1233.51 Company GHI
Cccc Cccc 2011-03-14 1215.98 Company DEF
I'm not sure which edition of Monarch you have (Standard or Pro), but I use Pro and I've never used Standard; therefore, if you do use standard, I'm not sure if it has the capability to perform external joins. If it doesn't, this solution isn't going to work for you.
Hope this helps or at least gives you an idea on how to resolve the issue.