@FT251 It's good to hear from you again. As I mentioned when we communicated through AS this summer the Wavelet does not truly contain a preamp in the proper sense of the word. It does contain a reliable and good quality volume control section however that is not the same as saying it has a full preamp. Whether it sound better overall compared to using an external full preamp (or DAC or streamer+DACD with a higher quality volume control section) is a function of many variables in the system including cables in between and other things.
Wavelet and Wavelet II are both capable of being a one-box solution taking a digital input, applying room correction then converting to analogue and providing an active crossover out to the matching Legacy speaker model (to the software revs loaded on Wavelet). Through a bank of XLR inputs (or you can use the RCA inputs), you can also run in any signal from the rest of the system be it a DAC with volume control or DAC->Preamp
or Phono or Tape Preamp->Preamp, etc...When you come in analog, the ADC onboard first converts the signal from analog to digital so the room correction can function and then, same as the above, the unit then uses its onboard 24/192 DAC to take the room-corrected outputs from the 64-bit DSP that are digital and convert them to analog being outputing through the active crossover portion of Wavelet.
As Wavelet is meant to fit into many different system permutations, when using analog inputs, there could be a case where your device upstream
has a very high signal level and would overload the analog inputs on Wavelet. The dip switches are meant to trim the input level if and when this
situation occurs. For several Esoteric preamps I've owned, a Coda/Saunders, a Classe CP-700 and one other, I've never had to use the dip switches as none of those input levels were too "hot" for the Wavelet inputs. There are preamps out there or DACs/other devices with volume
control sections that wind up having too hot an input level and you can mitigate this by trimming the input into Wavelet. Most people I known
of the few that have had to experiement find the -3db or -6db is about as much as needed though there are other devices out there with output
levels that necessitate a more substantial trimming of the inputs into Wavelet.
I always start with 0db when I change preamps and advocate others do the same. I would check your individual case with Legacy to see if they have different or addtional advice. I believe the manual also contains similar advice (start at 0db and only use the trims if.....).
On the subject of external versus internal amps,...their internal gen2 ICEdge amp modules for bass are actually excellent. It's in the mid-bass,
midrange and highs where I've found a real advantage using external amplification. Again, which is better is a function of many things, external amps in question (and preamp of course), cables you have on hand, etc.
Wavelet is meant as I understand it to be a great way to have a cost-effective system (all you need is a digital source) and also gives you other flexibility. On the other end of the scale you can experiment (and many do) with going direct in from a server or stream using digital and using Wavelet as an all in one device whereas you can also support a turntable and/or tape or other stack coming in analog with a proper preamp.
You can switch inputs with the web console app (also runs on Android or iPhone, tablets, etc) on the fly too as well as control any other aspect
of sound contours, DAC filters in or out, room correction off or on, and many other things. I won't repeat the whole manual here.
The best guidance I can offer is to continue planning your setup by reading the manual, get a basic mic stand so that you can properly position the calibrated measurement mic they supply perfectly when you run the setup sweeps, plan on break-in as there's a lot to break in terms of some audio circuitry, complex DAC and extremely power DSP. Break-in of upwards of 250-275 hours does help. Down the road when you can, plan on replacing the wall wart power supply with a good LPSU and good quality XLR3->XLR5 DC umbilical cable.
Have fun and enjoy!