Hi,
First of all, you should be able to install 3 in XE8. Are you using 3.15?
FlexCel 6.6 comes with a new reporting engine, which isn't a component, but as the rest of FlexCel 6, you create it in code directly.
First of all, read the document "MigratingFromFlexCel3.pdf" where it explains what I say here and more. Basically the new reports are similar to old one, but with much more functionality and a different syntax for tags: <#db.field> instead of ##db##field. There is also a converter to convert the reports to the new format in start menu->tms flexcel->tools
But the conversion isn't 100% automatic, so for a first thing, just install FlexCel 3 and use the old report. Then you can gradually change them to the new reports, but with time.