Well, reading your previous thread, I wouldn't run out and buy another drive just for scanning, unless you know your 3540 is faulty or you just want another drive anyways.. And, you cannot compare your 3540 scans to a LiteOn scan completely.
But, if you'd rather use something else to scan, good luck.. I am just saying you should test your 3500 burned discs on another 3540 first and see if it is, indeed, your 3540 giving drastically different readings than the other.
You have to keep in mind that each drive manufacturer's burners (and even seperate burners from the same company) reads discs differently also, and may generate very different scans. You cannot compare these scans.
However, I can say that if a disc scans fine on a bunch of different drives, and looks bad on another, that that drive is probably faulty or just a very poor reader..
The 3540 is a very good reader, so I would do some tests before deciding on another drive to scan with
Personally, I usually use my 3520 for scanning, because it isn't a great reader.. If it scans fine on there, it should be fine for most drives.