Conversion between two different lossy formats tends to create more loss and artifacts than re-encoding in the same format.
What bitrate, and have you tried re-encoding MP3 to MP3 at lower bitrate?
Most tools that do REAL, rely on compenents installed by RealPlayer / RealOne - from a company with a long association with spyware-infested software.
There may be other ways to get Real, such as Real alternative, Real at last - though bundlingthe required DLLs with another program is probably technically "warez".