I'm not sure what you mean by crossfeed. On the amp there is a "process/bypass" switch and a "filter/off" switch.
When I use the amp as preamp for the speakers I usually switch to to Bypass with Filter on. Filter off gives me a slightly more recessed sound. Leaving it on Bypass keeps the bass recessed more, its less in your face and bring that much more soundstage.
When used an headphone amp with AKG k501s, I use Filter on and Process. Filter on (compared to off) gives me a more upfront sound, it seems more detailed to me, but more smooth when the filter is off. As for the Process (switch which imo makes the most noticeable difference), it's hard to describe, so i'll help myself with some songs:
Keith Jarret - The Koln Concert Part 1 (piano only): Going from Bypass to Process adds a whole new dimension to the sound. The ground noise (barely hearable at loud volumes) is completely gone, and replaced by a more accurate sound. Each note played has more detail, less "jitter" (dunno if this is the right word) around it, its a clearer, cleaner sound all together.
Led Zeppelin - Stairway To Heaven: Wow. A click of the switch make a very noticeable difference here. I think it's pretty much the same as for the Keith Jarret piece, but the added dimension isnt something to forget. It gives a big feeling of soundstage with the AKG k501s. On bypass the vocals are close to my ears and the music feels very personal. On process, while the vocals stay close to the ear the other instruments seem to back away some, while their own volume stays balanced with vocals.
Kenny Burrell - Midnight Blue: Ok, with a softer jazz song, its a bit easier to catch. The Process switch on gives you a deeper bass, more detailed strings and drums.
Pink Floyd - Wish You Were Here: Wow again. I think my impression with the Led Zep song wasn't wrong, as I feel the same thing in this song. On bypass: I'm listening to headphones, the sound is on my ears. On process, the sound is all around my head.
In conclusion, I'd like to first of all say that these are my thoughts and opinions about music I like with my ears on my setup. There are a few things I mainly want to conclude about:
+ The filter switch gives a tiny bit more details when on, and the sound is slightly more up-front. This is rather hard to pick up tho.
+ The Process switch when on, in terms of better quality sound, helps a little. Again something more or less hard to catch, but it's imo more noticeable than the changes made by the Filter switch. In terms of "soundstage" (im not sure im using the right word) it does a great job. The music is literally surrounding my head instead of being simply in front. I really feel like each instrument is moved around n set to where it would be the most enjoyable, or at least more enjoyable than simply in front.
So, in my opinion, are those worth having on the amp? The filter switch, I could do without, the Process switch, I'd shoot anyone coming 50m near it while im listening to music.
I hope this helps a bit, it's hard for me (being french) to find the right vocabulary and since I am rather new to all this I am not sure you guys will understand what I tried saying ^^ Btw, feel free to correct anything I may have not said the right way, it'll help me not make the same mistakes in future "reviews", if a review that is.
EDIT: Gear used: Line out from nVidia nForce 2 soundcard to Headroom Home to AKG k501. I kept it simple, and chose the k501s which already have great soundstage because the amp adds to it alot. One more thing, this in no way described the changes the AMP itself does. it only compares the differences the switches on the amp does! I compare amp with switches off to amp with switches on, nothing else.
