Mos-fets or Bipolars

why does a bipolar amp offer more bass control and output versus a mos-fet? Will a bipolar amp be more stable in the bridged mode with each side of the amplifier seeing 2ohms when driving a 4ohm sub ? I just found out my Adcom 555mkII is a bipolar amp.Learn something new every day.
mosfet designs emulate tubes when it comes to playback...that said, many mosfet designs do have good bass control...cj as an example.
FET output parameters are somewhat similar to tubes and have also more limited impedance stability than bipolar transistors. The most negative factor of FETs is small gain that is even less than tube. That dictates a demand of multiple previous driving stages 2 or three before the actual output.
Bipolar transistors despite having less linear output characteristics are more stable to different impedance loads and have sufficient gain to be used with only one input stage(in-theory).
Currently, BJTs are more linear than MOSFETs - no contest. This may soon change with rapid advancements in lateral FETs but so far, the BJT is overall the most linear you can get. There is information on this topic in previous threads where I went into some detail on this point. This is why BJTs are most often used in amps actually. One of my research collegues is currently developing new doping techiniques in lateral FETs to improve their linearity and I have discussed this with him in detail.

FETs tend to be less stable but they are thermally better and can be used with little feedback if the painstaking task of matching them correctly is done. Transistor sound depends largely on circuit design (especially voltage-gain stage) so this point is hard to compare between the two types.

As far as bass control, it depends on the use of the transistors, SOA, and output impedance so it is hard to compare in general terms. Check the archives for more info. Take care - Arthur
Bipolars provide a higher current delivery than MOS-FET's, an important "bass control" factor.