I am wondering...Is there a speaker that will get quite loud (almost concert level volume) but still have soft smooth highs at higher volumes than most home audio speakers?
ATC play extremely loud (concert level) without any effort or strain. Highs are generally rolled off and they use robust silk dome tweeters that do not give you the usual ugly compressed/congested tweeter sound so common at higher levels - so no problem there on any of the models. Concert levels of 105 db SPL can be reached in a small room with the small SCM19's and a Bryston 4B with very low distortion (almost all other small monitor speakers distort badly before getting anywhere near these levels - SCM19's have the largest 6" woofer drive motor in the world)
However, depending on your music preferences - since ATC have a forward midrange (compared to most consumer speakers) then you may find them harsh in the midrange (not highs which are smooth)- this would be true of hyper-compressed mastered music such as Green Day, Red Hot Chilli Peppers, Metallica etc. - it will still sound great at lower volumes you just won't feel like cranking it for very long. People who like electronica, dance club music, classic rock (ACDC/INXS/Tom Petty/Led Zep etc), classical orchestral, country, Jazz, acoustic vocal tend to like ATC's - and mostly music professionals and artists who are intimately familiar with the sound of live music and instruments.
Another factor to consider is that since distortion is so very low at elevated levels and music sounds better louder - then the music will NOT seem loud as with other speakers - you may have an increasing tendency to crank it - so be careful with your ears & make sure your neighbors are far far away (it is the onset of distortion in other speakers that tends to limit how loud people play - distortion makes it "perceptively" loud in the same way as audio compression applied by mastering engineers does on some pop music).