Audio research or Manley 300B pre amp for Upgrade

Dear: my respected fellow audiogon members,

After deciding on my speaker upgrade, I am now about to seek some improvement in my audio system. As currently using audio aero capitole mk2 source conected directly to my manley snapper monoblock, I was advised by some friends that I should instead add a Pre amp. However, as I read through some of other members discussion, I found out that there were pros and cons regarding the pre amp usage after the aero. Some opinions hold it strong against pre amp addition as it will alter the purity of signal coming out of the aero, whereas some others believe that by adding pre amp there will be more body to the music as well as depth and staging width improvement.

Now, that I have the choice to tryout for a pre amp, should I go for the Audio research pre such as ls27 or even the reference 5, or should I go simpler by using the single ended manley neo-classic 300B pre amp (which doesn't have the XLR connection).. I lean towards all genre of musics (country, jazz, classical, soft rock) with exception of hard musics..

Would anyone share with me some great expertise and wisdoms.. Thanks all..