You can very easily mix the Pexi TMB with the sIII normal channel and get the best of both worlds!
sIII
Is a two channel version of the Marshall 18 watt which incorporates Treble, Midrange, Bass, Gain [volume] and Volume [master volume] and boost switch. The second channel is the Tremolo channel from the original design, without Tremolo. This amp is a medium gain amp and is voiced to do the early plexi/JTM45 sound very nicely. The range of tone is from spanky clean to Marshall grind. You can get a great Clapton Bluesbreaker sound and the Hendrix as well. This amp can handle Blues-Rock, Country & Reggae.
Plexi
Is based on the sIII design but voiced to sound period correct for a Marshall Plexi Lead. Screaming guitar lead tones at a much lower volume. The amp can thump and grind with less compressed tone than the other 18 watt variants. The normal Channel provides way more overdrive than most 18 watt normal channels while the Plexi channel is capable of the best clean sound we have ever heard come out of an 18 watter. With a pair of greenbacks, you'll be shocked how period correct it sounds. Crank up the gain and you are in crunch tone heaven. The clean boost just adds another dimension, it nails all those old AC-DC tones dead on and has way more gain on tap if needed.
Plexi MkII
Is based on the Plexi Super Lead preamp design with selected 'brown' components. This gets you very close to Eddie van Halen sound. Hot licks but with a very surprising clean tone with gain turned down. This baby can really move some air! Crank up the normal channel and it really gives up the goods! Lots of crunchy to high gain AC/DC tones for days. The TMB side cranked up is great going from clean to mean. Leave the gain low and crank the master and there is quite a lot of headroom with big fat cleans. The fat switch fattens up the TMB side and makes it a bit fuller spectrum of sound. Clip here:
http://www.unimind.us/TrinityPlexi2.mp3 TMB
Is also a two channel version of the Marshall 18 watt which incorporates a Treble, Midrange, Bass, Gain and Volume. The second channel is the Normal channel from the original 18 watt design. This amp is a high gain amp that does the 80s sound very nicely. It is intended for musicians who want plenty of grind. It does ZZTop very nicely. It is both responsive and aggressive. This amp does classic rock crunch to metal 'chugga-chugga' .
v6
Unique 18 watt adds switchable output tubes and boost to the sIII, Plexi or TMB. The sound is close to a Fender Deluxe and an 18 watt grafted together.
The channels can be jumped on all amps for more gain and tonal complexity. This can be done with a jumper cable or an ABY footswitch.