Couple things to consider when trying to achieve those tones:
1. The boost will provide extra compression in the preamp which not only smooth the top end but will also tighten the low end. So one thing you can do to reproduce that effect without a boost is to change your preamp tubes to a tube combination choosen for specific characteristics. For instance to emulate the preamp tube compression you get with a boost (especially at lower volumes) you can put something like an RFT ECC83 which has an earier breakup point and has a really aggressive characteristic but with very smooth highs. Then if you plug a Siemens ECC83 Long Plate in V2 you will add some richer harmonics and a very clear note definition. Then if you put something like a GE 12ax7a Long Plate in V3 for as very deep, defined bottom end that has a very clear punchy quality while still enhancing bass response. Then something like a Mullard 12ax7a in V6 to kill the buzzy charactersistics of the Recto and give the amp a sweeter, singing presence.
Going this route will help you further shape the way the amp sets up before you dial anything in. It really makes the amp your own and definitely sets it apart from other Rectos and other Roadsters. Case and point was this past 2 weeks i was on business trip in Cali and as usually hit up a bunch of music shops and played about 5 Roadsters over that time. None of those Roadsters could match what mine can do, and while the cab plays into that, the point is that tube change I made really set mine apart to what i wnat to hear in an amp. If your more curious about going this route check out my little experiement with my Roadster a few months back: http://forum.grailtone.com/ucp.php?i=pm&mode=view&f=0&p=81131
2. Gain/Presence/Mids settings are really important and are sometimes over looked. People tend to think to get the super heavy stuff you need to run the gain super high which isn't the case. Running the gain at and about 12 oclock or below will let your guitar's tone shine through the amp and will allow you to make the finer adjustments on the amp. if the gain is too high everything becomes mush no matter where the other settings are. The presence contols is another control that gets overused. I find the presence at or below 9 oclock will get you the punchy, smooth thump from the recto. As you get at or about 12 oclock the Recto fizz starts to emerge. Mids is the last setting that gets mis-used as people tend to scoop them which is fine for a mid heavy amp like a Marshall. Thing is the Recto is setup already scooped especially in the upper mids or singing mids. An OD is usually a great tool for adding back those upper mids but without using one, make sure you leave your mids at 11 oclock to 2 oclock.
3. Your cab and guitar pickups. To me there are 3 main pieces of gear that can make or break you tone. One is obviously your guitar and the pickups you use. A higher output pickup acts like an OD in a way by sending a hotter signal and depending on what the pickups eq curve looks like can also tighten the bass. The second piece is obviously the amp where the tubes and settings you use can dictate how your guitar translates into what we call "tone" once its outputted to the speakers. That said the last part is your cab/speakers. people tend to focus on what speakers are in the cab but i have found cab design can play just as important a role in how a cab sounds with an amp. My Mills cab to me is the perfect match to my recto and has the ability to handle any amount of bass while staying clear, powerful and strong. It is the best cab i've found for translating the tone my guitar and amp are trying to emaulate from my fingers. So my point here is your cab and pickups are just as important as your amp so dont overlook them.
4. Its been said in this post but I'll rehash the point.... you need to run this amp loud to get the tone your after WITHOUT a boost. They were built to be played loud and sound the best played loud. The reason for that is until you get to gig level volumes your preamp tubes arent at full compression which is more or less where a recto shines IMO. So unless you go with the idea of #1 or a boost, your going to need to run the sucker louder.
