Okay, so here are my thoughts on the Op-Amp rolling that I did... The Op-Amps that I tried were: NE5532N, NE5532P, BB OPA2640P, BB OPA627AU (Audio Jade 2 Mono to Dual), MUSES02, Burson V5i-D. I'll go from least favorite to favorite... NE5532N NE5532P: I forgot which one of these came with the Zishan. In any case, they sound very similar. Initially, I thought the original Op-Amp that came with the Zishan sounded good (and it does). Out of all, these sound the most "flat". Even keel throughout the sound spectrum but still pretty detailed and pretty good sound stage. I can see why they put it in there, it is the most neutral and uncolored (and probably inexpensive). BB OPA2604P: I think that this is the one that is soldered into the "transitional" Walnut V2. Everything gets more energetic here than the previous amp. Bass has more punch, highs get tinglier and vocals are more upfront and clear. Soundstage gets improved as a result of better separation of sounds. I could stop at this Op-Amp and be fine with it being in a $30 player. BB OPA627AU (Audio Jade 2 Mono to Dual): This Op-Amp was something like $9. Three times as much as the previous Op-Amps. This one sounded better than the OPA2604P. While having a similar sound signature (punchy, energetic, separated), it's vocals were a step forward and a bit clearer. I like this, good vocals and good punchy bass presence. I could definitely stop here and be fine with it in the Zishan. MUSES02 and Burson V5i: Let's just pause a moment and gain some perspective. The MUSES02 I ordered from Mouser Electronics (I didn't want to risk getting a fake on ebay) was $45. The Burson V5-i was $65 shipped from Burson from Australia. The Muses02 has the best clarity of all the Op-Amps. It's vocal and mid forward while losing a bit of that "Bass Pillow" that the Zishan naturally provides. It has great separation and is muscular, especially in the mid-bass region (the BB Op-Amps are more so in a lower part of the bass region). It gives more emphasis in the bass attack than the bloom. If you like James Jamerson and Motown, you will like where the emphasis is, or bass-as-counterpoint (ie- vocal Jazz). Because it's thick in the mids anything from the late 80's and earlier sound good. This is probably not for EDM...unless you like it clear and punchy and want it to sound like The Thompson Twins. The Burson V5-i is kind of a different animal from all the rest of these. You can follow the lineage upwards from the rest and then there is the V5i. The sound is sweet. The vocals are so sweet. It has great separation. It has a wonderful Bass. It can have great clarity. I say it CAN because it doesn't really in the Zishan. It's sounds good in there, but it's not being utilized properly and although I say it sounds good, I can't recommend it in there because...well, it's wasteful...and you might not like it because...well, it's different. I have added a picture of a small portable tube amp (Little Bear B4) because the Burson V5i actually sounds really good in here. It's being utilized where you can actually hear all the wonderful little things that Burson can offer. I'm sure this is not the best utilization of this OP-amp, but at least you can really "get it" when you listen to it in here. By the way, this amp is a really good companion to the Zishan Z1 and is only $65. And now since you have all of these Op-amps laying around, you might as well use them in something right? Haha.