I've been playing with other PDIP chips to try with my X-12. Tried an NE5534.
Using the LME chips included in the kit, running some EBTG vocals, I found the vocals to be more intimate, clear, capturing every nuance, breath, detail. Highs are crystal clear and detailed.
Using NE5534 chips, using the same music material, I found the vocals to be a bit farther away, not as intimate sounding as the LME chips. Still sounds good, but details and nuances were lost or cut back.
So... which one is better?
Both works and both will find use within your studio. One may be more suitable than the other, depending on your music material, or vocalist, or type of effect you're after.
If you want to add another flavor option to your preamp arsenal, I suggest having a couple of preamps with the LME chip, and another couple of preamps with the NE5534 chips.
... or use a Discrete Opamp. But if you want to play with the sound without spending $50-$70 for a DOA, try other PDIP chips like the NE5534 above.