Legacy Audio Impulse integrated amp (200W/Channel SS amp) - low volume issue

Nothing is wrong.  The Legacy amp used a volume control with more range.  Most volume controls on amps use the mid to upper range as that is where it sounds best.   The input sensitivity is probably lower on the Legacy Integrated by design.  You are fine. 

Sure, Thanks

I once had that Legacy integrated. Yes, it was built by Coda. The volume control on my amp had the same characteristics as you described. 
Very nice sounding amp; matched well with the Dynaudio Contour S1.4 I used then. Wish I would have kept that amp.

Welcome to the world of gain and sensitivity. Tube amps and preamps can have deceivingly high gains. This doesn't mean that they're more powerful than a solid state amp with lower gain!! 

Remember that most tube circuits were designed when sources were analog, and extra gain was useful. And lots of popular small-signal tube types have gobs of gain on tap. So it's easy to make tube gear that has tons of gain. 

But now we're in a digital world, where balanced DACs commonly push out 4V signals. The high gain preamps and power amps are no longer needed, or maybe even desired. So a lot of more modern SS designs forgo the extra gain stages. This means it can be difficult to even "max out" some SS amps when you're using an analog source. Meanwhile, a high sensitivity tube amp is easy to "max out" because it has simultaneously a lot of gain and not a lot of power reserves! 

In short - your Legacy amp is probably fine. It was designed with lower gain on purpose. 

Thank you stereo5, Valinar, mulveling, I am not worried that much anymore, l am getting same feedback from you all that it could be Gain may be because of the passive preamp section, and its quite normal behavior for this amp.

I will keep it in the 2nd system, meanwhile i compared it for little bit with the tube preamp and class D mono blocks and I still prefer tube preamp (with NOS Mullard) + Class D mono blocks but may need little longer comparison.