Similar to you I didn't really want to spend the same $$ for an amp as I did for the DAC. I'm sure there are good reasons to do so, and it's not because I don't believe an amp with a high price isn't worth it....it was mainly because I wasn't sure that the amp would alter or change the sound enough to justify the expense. Some may argue the amp is just as important, if not more, than the DAC, but if a DAC came with a reasonable amp I found it hard to justify (call it diminishing returns or my non-audiophile ear being unappreciative of the differences). When researching the ADI-2 I kept coming across posts and reviews where it was stacked with the THX....so I figured I'd at least look into it and it piqued my interest. Admittedly, part of the interest was the fact it was relatively cheap. ~$400 new, if I recall correctly, but even buying new would have to be on the secondhand market since Drop isn't selling them at the moment. I found a used one in like-new shape on eBay for $250 so figured what the heck, not much to lose if I wasn't a fan and wanted to unload it. A recommended set of $30 balanced cables from this site and I'm all-in for under $300.
Regarding your question....I wouldn't say the sound comparison is overly dramatic by any means. Admittedly, it's tough for me to truly A/B because I use EQ liberally and it's difficult to get them to be exactly the same to compare. I did try each with no EQ and the RME settings the same....and actually like the RME better (but didn't particularly like the sound from either, really). When I start tweaking the EQ I find I can hone it in better by using the THX. Can't really explain succinctly why - just sounds cleaner (sharper) going back and forth between the two. No idea why that is. Likely my lack of equalizing skills - it's probably the case that I could tweak the RME to sound exactly like the stack....who knows. I will say that the dead music spaces in the THX really are dead silent..the hiss and white noise is noticeably missing.
If I didn't have the THX I'd be perfectly fine with ADI alone, and will likely listen to it sans THX often just for something different. And if the THX was even 2x the price I'd probably unload it...but for the minimal (relative) cost I'm happy to have in the collection and honestly won't go looking for another DAC or amp because I love the sound of these. I do enjoy tweaking and thinking about the alternatives (DAC's, amps, headphones, etc) but at this point I think to make a real difference I'd either need to spend a lot more money and/or have someone who really knows how to set up EQ's and perfectly tweak the sound provide guidance.
