Integrated for bi-amping with AtmaSphere MA1s


My speakers (Ascendo ZF3s) have separate terminales for each driver.  I am currently using Atmasphere MA1s for the mids and tweets, and using a Pass X1 and Aleph3 for the woofers.  I'm also using a set of old Entec LF20 subwoofers crossed over with a Behringer Ultracurve pro for the really low frequencies.  I would like to replace the X1 and Aleph3 with a more powerful integrated, and am not sure what to use.  I've been away from this hobby for a number of years, but my first instinct when I think low frequencies is Krell.  The S300i looks intriguing, but I've read that it comes from a dark time in Krell's history, and may not be terribly reliable, and not up to the stnadards of low-frequency reproduction Krell is known for. 
Is this a good choice?  What else should I consider?
honest1
Thanks for the comments all.  I had been using the MA1s full range, with autoformers, but there was still some edge to the sound and softness to the bass.  Changing to bi-amping improved the bass and took the edge off the midrange.  I suppose all the fussing I'm going through to get them to work together is a sign the Ascendos are not the best match with the Atmaspheres, but they do provide the best sound I've ever had, and, in some ways,  some of the best sound I've ever heard anywhere.  But, of course, I'm always looking to improve.Heat can be an issue.  Most summers, there is a brief time I don't use the system much, but this summer seems worse than most.  I am thinking it might be a good idea to use the Aleph 3 during the hottest months to drive the whole speaker full range.
@honest1 have you tried tube rolling the 6SN7s in the MA-1? I was able to get the near perfect sound signature that I wanted by mixing different tubes, two of which Shuguang black treasures, those two especially emphasized the bass and took away any harshness from the highs. 
Yes, I m now running Sylvanias in the 3 middle positions, GE on the drivers, and RCA on the CCS.  The Sylvanias are good across the spectrum, the RCAs tone down the highs a bit.  I have not tried the Black Treasures, but I did get some rare Blue Glass Treasures (these were prototypes)when the Treasures first came out. 
This reminds me, I haven't been tube shopping in a while.  I should probably buy more NOS tubes before they completely disappear.
I own an older pair of Ascendo model Ms and although the speaker seems to function very well on amps of between 50 and 100 watts, much higher power really allows this speaker to breathe. I am a huge fan of Atmasphere amps but my concerns mirror your experience with this combo. Not a fan of class D but if you restrict this design to the low frequencies this might work well.