Arthur, you should contact the manufacturer to see if one the amps would allow you to run either tube, EL34 or KT88.
In many situations(such as in my Jadis amp), the manufacturer makes an EL34 version and a KT88 version. You can run both in the KT88 version, but just the smaller tubes in the EL34 amp. It has to do with biasing and the output transformers used on the amp. The KT88 version has much larger transformers, and cannot support either tube. Also, some amps will allow you to run a different output tube via a small component change, such as a resistor in the Jolida in the 302B and 502B.
With the EL34, you will not produce 50% of the KT88 power. Most of the time, the range is 20% - 35%, I normally tell people to expect about 1/3, and set them up for the worst. Often, the results are not so different. The one area where you will definitely notice the loss is the lower frequencies. The differences in tubes is quite apparent in the bass.
Personally, if it were me, I would first check with Unison to see if I could run EL34 in the KT88 amp, and find out whatever differences exist between the two products. If the differences in amplifiers extend to larger capacitors and/or transformers, then you are making a wise purchase by opting for the more expensive amp. That is definitely the one I would buy. If like the Jolida, however, the differences lie in a small parts difference, and the main difference is the output tube, I would opt for the cheaper amplifier. In that case, if the parts differences were minimal(if at all), you could always "upgrade" your amp to the more expensive version later via a local technician. On top of that, most people prefer sound of the EL34 Jolida 302B to the 6550 502B.
From you wish list, sounstaging and musicality, you could probably be happy with either. Depending on the KT88 you run, it can be quite a sweet tube. And, the bass is very good with this tube. Punchy. Ethereal, however, is really more in line with the EL34. Many people would not say this is accurate, but is sure is enjoyable.
The one question I would ask to you is, which version of the amp is the one that made such an indelible mark on you? Ultimately, that may be the one for you to buy. I am just guessing, but was it the EL34? Personally, I would set myself up for a long term purchase, and go for the amp where I could get whatever sound I desire.
In many situations(such as in my Jadis amp), the manufacturer makes an EL34 version and a KT88 version. You can run both in the KT88 version, but just the smaller tubes in the EL34 amp. It has to do with biasing and the output transformers used on the amp. The KT88 version has much larger transformers, and cannot support either tube. Also, some amps will allow you to run a different output tube via a small component change, such as a resistor in the Jolida in the 302B and 502B.
With the EL34, you will not produce 50% of the KT88 power. Most of the time, the range is 20% - 35%, I normally tell people to expect about 1/3, and set them up for the worst. Often, the results are not so different. The one area where you will definitely notice the loss is the lower frequencies. The differences in tubes is quite apparent in the bass.
Personally, if it were me, I would first check with Unison to see if I could run EL34 in the KT88 amp, and find out whatever differences exist between the two products. If the differences in amplifiers extend to larger capacitors and/or transformers, then you are making a wise purchase by opting for the more expensive amp. That is definitely the one I would buy. If like the Jolida, however, the differences lie in a small parts difference, and the main difference is the output tube, I would opt for the cheaper amplifier. In that case, if the parts differences were minimal(if at all), you could always "upgrade" your amp to the more expensive version later via a local technician. On top of that, most people prefer sound of the EL34 Jolida 302B to the 6550 502B.
From you wish list, sounstaging and musicality, you could probably be happy with either. Depending on the KT88 you run, it can be quite a sweet tube. And, the bass is very good with this tube. Punchy. Ethereal, however, is really more in line with the EL34. Many people would not say this is accurate, but is sure is enjoyable.
The one question I would ask to you is, which version of the amp is the one that made such an indelible mark on you? Ultimately, that may be the one for you to buy. I am just guessing, but was it the EL34? Personally, I would set myself up for a long term purchase, and go for the amp where I could get whatever sound I desire.