I am not Ja_zz (obviously), but I have just done a comparison between a Unison Research S6 and a quality Korato EL84 based tube amp which I imagine would be similar to the Leben outputting 15w. I have also listened to a Leben many years ago in a different system, in a very awkward room and with AudioNote speakers. I thought the sound was really quite poor, the bass was all over the place, but with regards to my system:
Listening with ProAc Response 2.5 speakers and Meridian 507 CDP and Technics 1210GR. I listen nearfield'ish, within 3 metres and the room is 3.5m wide, 9m long and about 5m high at its peak.
I had the Korato in the system for a few weeks first, it is a cute looking unit and that was certainly part of the appeal. It had recently been re-tubed and had some quality caps fitted along with a good service. So I know it was in good form.
It gave a very nice crisp and sprightly sound. It did draw me in and had good imaging, but the sound stage was quite small. Whilst only 15 watts the sound was pretty big and could go loud, but weight was lacking and obviously clipping occurred pretty early on where voices became hard. Kept in check though, the midrange was very dynamic and sweet, really the party piece of this amp. However, the ProAc's are rated at 85db at best, but are a benign load. What bass there was, was really fast and fairly layered and detailed but not a lot of weight. The ProAc's are rear ported and need control, on busier tracks the flow was lost.
If listening to simple Jazz and acoustic recordings I would say it is very nice, a really good tone and toe tapping quality, but just missing weight.
So, the S6 came along a bit later and it's a huge thing. Marketing pictures on the internet don't really portray it's size. It is also 25KG, so probably twice the weight of the Leben and this Korato.
This unit could be nearly 20 years old and appears to have Unison tubes, which may well be the originals, it's hard to say. Anyway, it was like listening to a big cloud of music at first. Put it this way, I drive a Volvo saloon and the guy who lent it me drives a BMW M2. He let me take it for a spin, probably nearly 300bhp with a driving position akin to a LeMans car. The Unison was the Volvo, not the BMW.
There was no real soundstage, the bass was big and slow and an overall impression of slowness and warmth.
I was relaxed but was getting bored, so I put back in the Korato. I know this thing takes about 30 mins to warm up, but not a big difference in sound is noticed after this time. However, the sound was more anemic and grating, I wasn't relaxing with the music as much as I was with the Unison, which is what I needed to do this night, relax that is.
It was about 9pm when I put the Unison back in, unfortunately it was 2:30am when I turned it off. After a while, the soundstage became much larger and accurate, I was certainly front row. I had instruments being played to the very right of me and all around, never have I experienced this before to such an extent. The music was still presented with a big and bold sound, but the highs were also just right, perhaps a bit too much when listening to The Fall, but this wouldn't be the best recording anyway. It made everything very listenable and totally enjoyable, was it accurate, possibly not. I listened to everything from house, jazz, rock. Mids perhaps not as sweet that as with the Korato, but they had a nice weight to them and I didn't feel it was slow or boring. The House music bass lines were not well represented, they got a little out of focus, but everything else was to me pretty faultless. I was grinning a lot and only when my wife called from the bedroom at the other side of the house, to ask what on earth am I doing playing music that loud at 2:30am on a school night, did I retire to bed.
This was only last night, so I will try and give perhaps a more balanced opinion over the coming week or so, but so far so good for the Unison. I think it proves that the Unison is not so critical of speaker pairing where as the Leben and other low power EL84s are, which is no surprise. Everything you read in forums about the lower power EL84s is probably accurate, what isn't so accurate is that you need high power to get volume and bass out of low sensitivity speakers unless you have a big room and sit far away.
