The actual frequency is 6739.0 USB. It is part of the HF-GCS (High Frequency Global Communications System). It is military, it can be accessed by any US service but is predominantly US Air Force.
There are sites located all around the World, and it is not unusual to hear a pronounced echo on the signal, this echo is caused by you receiving more than one station at the same time.
Frequencies to watch for this traffic are 4724, 6739, 8992, 11175, 13200, and 15016 kHz, all are in USB mode. There are other frequencies as well, but those are the most active. It is common, in fact it is the norm, to hear the same message on multiple frequencies at the same time.
Without more detail it is impossible to tell exactly what kind of message you heard, there are several common types, but it is quite likely it was indeed an EAM.
T!