Is my amp the problem?

Good comments by Auxinput.  I just noticed something further about the Modwright amp.  I had stated its input impedance as being 23K, because the impedance is indicated on its webpage as "Min. 15K 50Khz; 23K 1Khz," and I considered the 50 kHz impedance to be irrelevant.  Although I wondered a little why he would bother specifying a 50 kHz impedance.  However I now see that its manual (in contrast to the webpage) indicates an input impedance of "Min. 15K at 50Hz [not kHz]; 23K at 1Khz."

So that makes it all the more important to avoid requiring the LS100 to drive a low input impedance device in addition to the Modwright amp.  My suggestion at this point is that you communicate with Dan and ask him what minimum load impedance he would recommend be used with the LS100.  While you're at it, also ask him to clarify if the amp's specified input impedance applies to its balanced input or its unbalanced input or both.

Regards,
-- Al
   

One thing one thing to mention ,the amplifier is nothing special to begin within 
for sure invest in a known product such as Wyred 4 sound  ,Pass labs 1st watt
evrn Nad ,or tons of other proven companies.
iwith your speakers  who built them and how to know if  they knew about proper 
speaker building Xovers very important and not easy to get right .usjng a online 
computer program Essential . I have bought from little companies before I won't name ,that had no clue ,no matter what cable or amp,preamp upgrade 
it was not seamless I tried my own Xover upgrading since I have modded caps, resistors,inductors  for years f the design is flawed yiu can hear it .
with the price of new Elac products ,and evrn lower priced excellent JL audio 
subs for under $1k  you can build a great starter system for under $2-3 k for Everything including digital and cables. Just advise I have had single drivers
and passive is not always so a inductor  or resistors change the driver in some fashion.seek local Audiophiles  many would love to help including myself .
where are you located? Myself New England.If you don't know Ask I have been doing this for 40 years and still learning . No one  knows everything !!

Uh- all good suggestions, but before you do anything else, check to see that the woofers are in phase.

That is to say, if the red connection on the back of the amp is connected to the plus terminal of the speaker, that such is also the case with the other channel. This way both speakers are pushing and pulling in unison. Otherwise they are fighting each other, and you would have some pretty 'blah' bass!