Is polk Lsi15 too big for my 20x13x8 room?

Your room is not too big for full range speakers played at reasonable levels. That is not to say that it can't potentially be over driven but that applies to most rooms.

I have full range speakers in a similar sized room and have no problem whatsoever not inherrent in the size of the room, which would apply to all speakers (nulls and nodes caused by room dimensions). But, proper set up is critical and your listening distance of 11 feet in that sized room suggests to me that you set up may no be optimum. If you haven't already done so you might greatly improve you sound by doing some research on set up.

Regarding amps and volume to get the music to open up, many dynamic (cone based) speakers sound best at medium to loud volumes. If you like lower volume levels you may want to investigate speakers which present a fuller sounds sound spectrum at lower levels. Remember, everything! has tradeoffs.

I can only suggest those things I have listened to at length in my own home - you can check my systems and associated threads for where I've been sonically speaking. So FWIW, I'm presently using Tyler Linbrook Signature 1 full range 1 piece floor standing systems and I'm driving them to my satisfaction with a Primaluna Prologue 3 & 5 (35wt amp). At moderate volume, between 76db and 85 db the sound at the listening position is full, warm, and detailed without being in the least bright or etched. These sound much more full ranged at low volume than any of their predecessors (in my home) with the exception of the Quads, however proper placement, dynamics, and amplification issues keep me from recommending Quads.

The Tylers are capable of playing quite loud and the side benefit with this is, in my system at least, when played loud the highs don't drive you out of the room. I suspect this may have much to do with the tweeter used in this model. There have been a lot of comments on Tylers stuff in this forum and I can hardly recall a negative reaction to them.

For a pair of used Tyler's and if you want to save money a Primaluna Prologue 2 (3800 & 1450 respectively) you can have a great music system that will be hard to beat. And they will sound great in your room which is within 5 inches of the size of mine.

If this is in your budget range, do some more research for confirmation. Tylers can be bought on trial and if you don't like the Primaluna its a dead easy resale item.

Odnok, The speakers are the key to low volume listening. The amp should not be very important EXCEPT as to the tone it imparts to the speaker at low levels. I'm not a fan of SS amps, and contrary to common belief they are not maintanence free. Big tube amps can be a hassle and even small ones require a bit of routine maintence, but the ones I suggested are about as idiot proof and low maintenance as you can get. There are no spec's which would reveal a speakers ability to play at low levels.

As to starting a new thread, this has been discussed several times in the last few months. You may do a little research and see if you can pull up those threads. You can probably get some feed back from Tyler users regarding Tylers and SS stuff. I know I've seen several users say they preferred ss.

If I can help...........

Odnok, Start a new thread - as it is only folks with experience with room set up are likely to note your present post and respond.

Odnok, I assume you asking about the Tyler Linbrook Monitors.....

Based on your comments regarding sound level you would listen at I would think a tube amp of 35 wts such as the Primaluna would work well. But it won't 'rock out'.

A better person to ask is Ty - he will give you the best advise in this area. The secret is in the impedence curve and Ty knows exactly what that is. I don't.

FWIW, there are several other threads on 'low level listening' you should read which may give you more help in making your decision. I'm in the camp whech believes that low level listening pleasure is derived from speakers which have very high resolution, you can hear all of the detail in the recording without the need to have high volume. At least that has been my experience.