I contacted ESS and they were very helpful, recommended an auxiliary file limit of 20sec, I loaded a file that ran 27sec which ran fine, then asked ESS if I could load a longer file if I deleted the second engine sound, they replied (within seconds) that it should be possible, so will give it a try.
But very pleased with the sound editor that is built into the ESS RC Plus software.
I am using car engine sounds and can choose from dozens of different engines, I was looking for a vintage V8, but the nearest I've found is a 1969 Mustang, not bad.
For those looking for ship sounds the choice is very limited, but I was very impressed with their 5000hp ship engine sound.
A very pleasing development is that the RC Plus software now allows one to listen to a sample of all their sounds without connecting a sound unit.
The RC Plus software is a free download but is only available for Windows and gives a great insight into the performance of the sound modules without spending money.
The download has a minor drawback in that one of the prompt screens is in Chinese (select the left hand box)
Have fun
[size=78%] [/size]