Hi pdskosmowski and welcome to Insiders.
Here is a thread and links for you to review, hope this helps.
I'm not sure what you mean by using Marriott's airline service, but I think you are looking at the 'Marriott Rewards Air and Car' program. One pays a significantly higher price in points than using a point ticket directly with the airline.
Also, in the program that can be used to transfer Rewards points to miles and directly to the airline of your choice there is a significant devaluation of the Marriott rewards points for doing so.
There is another 'Travel Package' program that allows for a transfer of Rewards points to the airline of your choice on a one point equals one mile basis and no devaluation of your Rewards points for the transfer.
Here is the program page: Flight and Hotel Packages | Marriott Hotel Packages
If you use the travel package setup you can transfer points to the airline of your choice and get full value of your Marriott Rewards points applied to your airline. The program also gets you a 7 night stay certificate at the same time, but you can ask them to send you the certificate (or put it into your account page) and HOLD the certificate to use at a later time if you are not ready to book a hotel with a certificate when you do the transfer.
So, points become the miles at full value and they go directly to your airline account and the certificate is available to use when you want to. The certificate will have an expiration date though (most likely a year later).
Example using the program page breakdown for a 50,000 mile transfer to American Airlines and a 7 night certificate at a category 6 hotel:
6 nights at 30,000 points per night (one night is free based on the redeem points for four nights and get one night free program making it a seven night certificate) equals 180,000 points for the 7 night certificate and 50,000 points transferred into 50,000 miles on your American Airlines account for a total of 230,000 points for the package. Reward Points transferred to miles in this plan are equal in value and you don't have the significant devaluation as you will in a direct point to miles transfer.
Hope this helps!