I assume you're looking at one of the ALX/EX train connections on this route (rather than anything involving a DB Express Bus). There are no Europa-Spezial discounted fares on these trains (as such fares are generally only valid for cross-border travel on ICE/IC/ECs - and the ALX/EX train counts as a local (NV) train in Germany). (There are discounted second-class fares on the DB Express Bus, but no first class, as it's a second-class-only service).

If you were travelling in second-class, then there are two ways of getting a slight discount on the ALX/EX journey (quoted fare of €47.50):
- The 'Prague Special' ticket for €43 from Regensburg
- Combining a Bayern-Bohmen ticket with a CD ticket - see here for details

Note that on the ALX/EX trains, first-class isn't that different to second-class (there's no station lounge access, nor complimentary meal service or anything like that). However, the compartments may be slightly more spacious, should be less crowded, and may have a power supply for laptops, etc.

Correct - there is no way of doing self-print tickets for your route:
- The ALX/EX service is not operated by DB, and therefore DB self-print tickets are not recognised (nor issued). However, there is no discount for buying in advance (although there may be a €2 surcharge for buying at a DB ticket counter rather than from a machine or on the train). So, there shouldn't be any problem with just buying at the station on the day of travel (unless you really want seat reservations - see below).

- DB will issue self-print tickets for Berlin-Prague (and presumably Berlin-Prague-Berlin return) but NOT Prague-Berlin. See this post, and others in the same thread, for an explanation of this. You may find that www.cd.cz will issue self-print tickets for Prague-Berlin, but I haven't checked. If you want to book in advance, and collect tickets at the station (rather than getting them by post) you should be able to do this if you call DB. They will make the booking for you, and then give you a reference number which, combined with your credit card, will enable you to collect the ticket from any DB ticket machine in Germany. (ie: so you'd have to collect the Prague-Berlin ticket while you're in Regensburg - you could not collect it in Prague).

- For the ALX/EX Regensburg - Prague, I had thought there was no possibility (or need) to make seat reservations. However, the Prague Special link above suggests seat reservations are possible - without saying how they can be made. I thought first class on these trains was mainly closed 6-seat compartments, but maybe there are some open saloons as well.

- For the Prague-Berlin EC, I'm not sure. However, if you book over the phone, they should be easily able to select whichever seats you want. (Choose the right hand side of the train if possible, for the best views going along the Elbe between Prague and Dresden...)