Cykeric, I'm a little confused, I did GON reviews on both the DAC 1-MK4 and the Drive 1-MK2 which compared them to the first generation AA pieces, not the Reference Tube Hybrid DAC. Take a look at them, if you have not already.
Regarding your question about what is the difference between the tube DAC 11 and the SE version, the SE version uses some higher tolerance parts and supplies you with what are called special "NOS quality tubes". Well, at least the SE unit I heard came with JJ 12AX7 tubes, which ain't special, not NOS and sound like crap. The sonic difference between my DAC 11 and the SE version was my DAC sounded better with the tubes I use, NOS 12AX7 Amerex Bugle Boy long plate G getters. If I was buying new right now I still would buy the tube DAC 11 which sells for around $1200.00 less then the tube DAC 11 SE and go out and buy some great NOS tubes, cost would be around three to four hundred dollars, save alot of money and still have a DAC that out performs the more expensive model. This DAC's sonic performance is greatly effected by what tubes you use. So for my money I want to pick what NOS tubes that give me what sonics I'm looking for. So, in my opinion the change in a few parts or their working tolerances did not make any significant sonic inprovement, but without casting aspersions towards either AA or the US importer the DAC SE I experienced did not come supplied with NOS tubes, I guess the JJ's are better then the EH stock tubes in the DAC 11 but they both are crappy sounding, and you are supposely spending some of the extra cost on NOS tubes provided by AA. Can't answer your question regarding the top cover, the units I have seen all have the craved out tube design.
Regarding your question about what is the difference between the tube DAC 11 and the SE version, the SE version uses some higher tolerance parts and supplies you with what are called special "NOS quality tubes". Well, at least the SE unit I heard came with JJ 12AX7 tubes, which ain't special, not NOS and sound like crap. The sonic difference between my DAC 11 and the SE version was my DAC sounded better with the tubes I use, NOS 12AX7 Amerex Bugle Boy long plate G getters. If I was buying new right now I still would buy the tube DAC 11 which sells for around $1200.00 less then the tube DAC 11 SE and go out and buy some great NOS tubes, cost would be around three to four hundred dollars, save alot of money and still have a DAC that out performs the more expensive model. This DAC's sonic performance is greatly effected by what tubes you use. So for my money I want to pick what NOS tubes that give me what sonics I'm looking for. So, in my opinion the change in a few parts or their working tolerances did not make any significant sonic inprovement, but without casting aspersions towards either AA or the US importer the DAC SE I experienced did not come supplied with NOS tubes, I guess the JJ's are better then the EH stock tubes in the DAC 11 but they both are crappy sounding, and you are supposely spending some of the extra cost on NOS tubes provided by AA. Can't answer your question regarding the top cover, the units I have seen all have the craved out tube design.