You can make sure that the EPROM chip is the most current (version 4.03 was the last version made for Type I ADAT's, this will make it work with XT's. You can check that by pressing the 'set locate' and 'Fast Forward' buttons at the same time. A number will display in the time LCD display on the machine)
The other upgrade you are referring to has to do with replacing the 1/4" input and output jacks on the unit. First, it will make them 1/4' TRS instead of TS. It is also claimed by the manufacture of this board that it greatly improves the converters also. Since I have NEVER received a email response from the company that makes these boards, I can't tell you a thing about them.
Go to www.alesis.com and click on 3rd Party Developers and find the link to Horizon for more info.