So you use the K7XX with the vali2? What's your favorite tube accompaniment?
Right now I've got in a 6922EH and I'm not really noticing anything super impressive in terms of altered sound, pretty comparable to going straight into my headphone out minus the volume of course, and I've got ~30 hrs burn in. I've got a few days before I can't return the Vali2 anymore and seriously considering getting the Little Dot i+ instead.
@bguags Quick answer is the Reflector 6N3P-E, but that requires an adapter. There are so many good tube choices possible, but here's a recent discussion on that group of tubes:
http://www.head-fi.org/t/673709/schiit-lyr-tube-rollers/9975#post_12894833
However the immediate issue appears to be the deadline for returning the Vali2, and purchasing/shipping a new tube may not be feasible.
I believe the real issue is your source and feed to the amp. In the other thread where you initially posted (http://www.head-fi.org/t/793982/vali-2-tube-rolling/615#post_12898338), you confirmed that you are using the headphone out into the Vali2. The signal has been converted and amplified by your laptop, and then is amplified again by the Vali2. The quality limit of the signal is established by the laptop. Additionally, every stage of amplification adds some distortion. True, you can get a tube that will 'alter' the sound but this approach is not consistent with the goals you indicated in the first thread, which were to improve the detail resolution and soundstage. (You correctly answered your own question, the Vali2 is just increasing the volume.) If you really want to just 'alter' the sound, you can choose one of the tubes that will add some noticeable distortion, some do enjoy the effect.
If you want to improve the detail resolution, hear more of the ambient/spatial cues, improve the 3D aural image, then you may need to improve the quality of the source signal to the Vali2. You can do that by adding a DAC, or using a decent quality DAP, which may be less expensive. If you have USB connections in that chain, there is also the possibility of some additional expenditure to clean the USB signal or convert it to SPDIF (Coax or Toslink).
Not sure exactly what you are working with for the source, but you want to consider the entire audio chain, it is possible that the weak link is not the tube.
Last thing, I am not familiar with the LDi amp, only what I've read. I'm sure it's also a very good amp for your needs, I just don't have any experience with it.