IMHO the cables should be done last because they should complement the sound not define it. Your question was where should you start that will make the biggest impact.
This is like asking which is better solid state or tube. There are all kinds of reasons and all kinds of opinions but there is no absolute way to termining a clear winner. There is so much subjectivity and emotion in music what is one person's heaven is another person's hell. Just look at today's thread about ugliest speaker...some people say the Avant Guard's are ugly and one person sees them as art. Who is to say? Even though I think they are ugly...hey what does my opinion matter, whatever floats your boat.
A couple of comments below but I am not saying which should be changed first because order is like beauty. The CD player and preamp need to be addressed so just pick one and go (further comment on cables later).
If you are willing to spend the kind of money needed to buy the 380s then you can afford the best pre-amps in the world (bar just a couple of crazy expensive 2 box units). I think you need to understand what kind of sound you are looking for. There is no "best" in anything and you have started down a certain sonic trail by getting the Martin Login's and using the ML amp.
You may want to get more of the same or look for something that brings more warmth and richness to the presentation. If you don't have a dealer(s) in town where you can audition the equipment, you should be able to hook up with some store long distance that will accomidate your search. Unless you are bucks up and can afford to buy and resell you need to spend some time with the new unit(s) in your system.
Some of the hotest names in Pre-amps right now(all the same or less the 380s price range)are: Hovland, CJ, CAT, Blue Circle. Earlier this week there was a thread about a pre-amp many are saying is as good as you can get out there and it is only $2100-$2500. If I had the cash, I would look into this...http://www.cantech.net.au/~supra/preamps.html. See the thread "Preamp Deal of the Century".
All these companies are making world class gear so the choice comes down to one of personal taste. No one, no matter how well meaning, can tell you one item is clearly better than another. If it is better to you, it is better because your listening enjoyment is the most important thing.
It really is a toss up which is more "important" the CD Player or the preamp. Remember, a signal can not get any better once it leaves a component, it can only degrad less or have added "character". So, starting with your CD player, once it leaves the outs on the player it will never get better, and then once it travels accross the cable it can never get better. It may appear to be improved but technically it can not improve it can be altered but not improved. {actually it can't get any better than the software recording itself but you get the idea). There have been a number of good threads recently talking about the best in one box CD players which include discriptions of sonic characteristics. At this point you may want to decide if you want to do something with SACD or DVD-A and that will narrow your choices. I understand that you could get the best of both worlds if you buy the Sony SCD-1 and have it tweeked out (you can also find this in recent threads).
CD players....again, depends on how much you want to spend and what characteristics you want in your presentation. The Martin logins seem to like a lot of power so the ML 336 is probably a good choice as far as that goes, so if you like the characteristics of the ML then you are good to go. For me, ML sounds just a tad dark and all the times I have heard them they seem lifeless and all the ML gear seems to have the same signature. Now lots of people think they are the beat-all-to-end-all so this is just preference. I bring this up to illustrate the need to define what YOU like.
Even if you like the ML sound you may not want it throughout your system...you know, too much of a good thing.
As far as cables go, again, I have been taught that cables, racks, power management, and the like should be saved to finish out your systems unique sound. I am not saying the cable can't impact the sound a great deal, quite the contary it can have a big impact, however, if you start messing with the cables in the middle of your main component chagnes you will have a hard time seeing what piece is doing what to the overall sound.
Even with this said, you may want to buy some better cables than you now have while you evaluate because the cable you are now listening with isn't the best. You may want to start with midline cable from Van Den Hul or Nordost. Van Den Hul is little warmer and laid back (compared to Nordost) and Nordost is considered very netural and fast. Whatever you choose, make sure you understand the characteristic it will bring to your system and don't mess with them as you go through your review.
Good listening,
cd
