In my opinion, and only my opinion, a room 13ft x 10ft is a bit small for 2x8" bass drivers. And room size relative to speaker size is just that, an opinion, not a hard and fast rule.
While the
Rubicon 6 would be fantastic speakers, they are a bit steep at £3000/pr. If you can afford that - fine. But at least consider the
Opticon 6 at about £1200/pr.
Dali Opticon 6 Speakers (Pair)
But I would not call the
DALI laid-back or mellow. From my very limited exposure, they seem to have a good strong Mid/High presence, though not overbearing or excessive. That would great for Movies, but less so for music. Again, just one man's opinion. I'm sure the Dali are also great for music.
If you want a more mellow smooth speakers, and you've got some cash to spend, consider
Wharfedale REVA. Though even the
REVA are well under your budget -
Wharfedale Reva-4 Speakers (Pair)
In roughly the £2000/pr range, if you want speaker that have good Mid/High presence that is not overbearing, yet have very clear controlled bass, then consider the highly rated
FOCAL speakers -
Focal Aria 936 Speakers (Pair)
Focal Aria 926 Speakers (Pair)
You might also what to consider
QUAD speakers. I would expect them to have a sound closer to what I interpret you are looking for -
Quad Z-3 Speakers (Pair)
Quad S5 Speakers (Pair)
You might also want to consider the
Bowers-Wilkins (B&W) CM series -
http://www.superfi.co.uk/p-15688-bw-cm9-s2-floorstanding-speakers-pair.aspx
http://www.superfi.co.uk/p-15687-bw-cm10-s2-floorstanding-speakers-pair.aspx
The outboard tweeter on the
CM-10-S2 does amazing things to the sound stage, but it is a pretty expensive speaker. However, I have auditioned the
CM-9-S2 and they sound pretty good.
If you are set o
DALI, then I think in that relatively small room, the choices are the
Opticon 6 or the
Rubicon 6. I can't say with certainty, but the
Opticon 8 seem a bit big for a 13ft x 10ft room.
In the end it is up to you to decide whether the
Opticon 8 are too big for your room. They will certainly work, the question is how well will they work. But most certainly, the
Dali Opticon 6 and the
Rubicon 6 would work.
All of the other speaker I've recommended all have 6.5' (165mm) bass drivers with the exception of the Quad Z3, which have 175mm (6.9" or 7").
If you are going for pure finesse, detail, and subtelity, and you have £3000/pr to spend, few could fault the
Rubicon 6. But that is a pretty steep price. Similar but at a lower price, the
Focal Aria.
If you would like to reduce the budget, the
Opticon 6, the
REVA 4, and the
Quad S5 are all very good speakers in roughly the £1200 to £1500 range.
And it is certainly worth auditioning the B&W CM9 at £2000/pr. Well balanced and detailed speaker.
Unfortunately, I have ZERO knowledge, experience, and feedback on the
Roger LS55, so I can't comment on them, and I can't imagine speakers that might have a similar sound. I did find this video though, for what little it might be worth.
With Tube/Valve Amp, I would be inclined to look at more efficient speakers. Try to get a Sensitivity as close to 90db or more as possible. While speakers in the mid-80's will work, I think you will be more pleased with higher efficiency speakers. Even the difference between 87db and 90db is like doubling the power.
Lastly do you have any idea what the
Rogers LS55 cost new? That might help lend some perspective.
Just a few thoughts.
Steve/bluewizard